Codebook-based signal transmission/reception method in multi-antenna wireless communication system, and device for same

ABSTRACT

Disclosed are a codebook-based signal transmission/reception method in a multi-antenna wireless communication system, and a device for same. Specifically, provided is a method by which a terminal transmits/receives a signal on the basis of a codebook, in a 2-dimensional multi-antenna wireless communication system, comprising the steps of: receiving a channel state information reference signal (CSI-RS) from a base station, via a multi-antenna port; and reporting channel state information to the base station. The channel state information comprises a precoding matrix indicator (PMI) for indicating a precoding matrix. The PMI comprises a first PMI for selecting a precoding matrix set from a codebook, and a second PMI for selecting one precoding matrix from the precoding matrix set. The pair of the first dimensional index and second dimensional index of the precoding matrix belonging to the precoding matrix set is (x, y), (x+2, y), (x, y+1), (x+1, y+1), x and y being whole numbers that are not negative.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more specifically, relates to a method of transmitting and receivingsignals on the basis of a codebook in a 3-dimensional multi-inputmulti-output (3D MIMO) system in which a 2-dimensional active antennasystem (2D AAS) is installed, and a device therefor.

BACKGROUND ART

Mobile communication systems have been developed to provide voiceservices, while guaranteeing user activity. Service coverage of mobilecommunication systems, however, has extended even to data services, aswell as voice services, and currently, an explosive increase in traffichas resulted in shortage of resource and user demand for a high speedservices, requiring advanced mobile communication systems.

The requirements of the next-generation mobile communication system mayinclude supporting huge data traffic, a remarkable increase in thetransfer rate of each user, the accommodation of a significantlyincreased number of connection devices, very low end-to-end latency, andhigh energy efficiency. To this end, various techniques, such as smallcell enhancement, dual connectivity, massive Multiple Input MultipleOutput (MIMO), in-band full duplex, non-orthogonal multiple access(NOMA), supporting super-wide band, and device networking, have beenresearched.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method of configuringa codebook in a wireless communication system supporting 2D-AAS based 3DMIMO.

In addition, an object of the present invention is to provide a methodof configuring a codebook using a discrete Fourier transform (DFT)matrix in a wireless communication system supporting 2D-AAS based 3DMIMO.

Furthermore, an object of the present invention is to provide a methodof transmitting and receiving signals on the basis of a codebook in awireless communication system supporting 2D-AAS based 3D MIMO.

Technological objects to be achieved by the present invention are notlimited to the aforementioned objects, and other objects that have notbeen described may be clearly understood by a person having ordinaryskill in the art to which the present invention pertains from thefollowing description.

Technical Solution

In an aspect of the present invention, a method for transmitting andreceiving a signal by a UE based on a codebook in a 2-dimensionalmulti-antenna wireless communication system includes: receiving achannel state information-reference signal (CSI-RS) from an eNB throughmultiple antenna ports; and reporting channel state information to theeNB, wherein the channel state information includes a precoding matrixindicator (PMI), the PMI includes a first PMI for selecting a precodingmatrix set from the codebook and a second PMI for selecting a precodingmatrix from the precoding matrix set, pairs of indexes of a firstdimension and indexes of a second dimension of precoding matricesbelonging to the precoding matrix set are (x,y), (x+2,y), (x,y+1) and(x+1,y+1), and x and y are integers which are not negative numbers.

In another aspect of the present invention, a method for transmittingand receiving a signal by an eNB on the basis of a codebook in a2-dimensional multi-antenna wireless communication system includes:transmitting a CSI-RS to a UE through multiple antenna ports; andreceiving channel state information from the UE, wherein the channelstate information includes a precoding matrix indicator (PMI), the PMIincludes a first PMI for selecting a precoding matrix set from thecodebook and a second PMI for selecting a precoding matrix from theprecoding matrix set, pairs of indexes of a first dimension and indexesof a second dimension of precoding matrices belonging to the precodingmatrix set are (x,y), (x+2,y), (x,y+1) and (x+1,y+1), and x and y areintegers which are not negative numbers.

Preferably, a spacing between precoding matrix sets adjacent in thedirection of the first dimension may be 2.

Preferably, the codebook may be composed of a precoding matrix generatedbased on the Kronecker product of a first matrix for first dimensionantenna ports and a second matrix for second dimension antenna ports,and the first matrix may be specified by a first dimension index of theprecoding matrix and the second matrix is specified by a seconddimension index of the precoding matrix.

Preferably, values of first dimension indexes and second dimensionindexes of precoding matrices belonging to the precoding matrix set maybe determined based on the first PMI.

Preferably, a factor for controlling phases between a first polarizationantenna port and a second polarization antenna port may be determined asone of {1,

$\left. {{\exp \left( {j\frac{\pi}{2}} \right)},{\exp \left( {j\frac{2\pi}{2}} \right)},{\exp \left( {j\frac{3\pi}{2}} \right)}} \right\}$

based on the second PMI in a cross-polarization antenna.

Preferably, a total number of precoding matrices constituting thecodebook may be determined by the product of the number of antenna portshaving the same polarization in the first dimension, the number ofantenna ports having the same polarization in the second dimension, anoversampling factor used in the first dimension and an oversamplingfactor used in the second dimension.

Preferably, the first matrix may be composed of one or more columnsselected from a DFT (Discrete Fourier Transform) matrix generatedaccording to the equation below,

$\begin{matrix}{{D_{({mn})}^{N_{h} \times N_{h}Q_{h}} = {\frac{1}{\sqrt{N_{h}}}e^{j\frac{2{\pi {({m - 1})}}{({n - 1})}}{N_{h}Q_{h}}}}},{m = 1},2,\cdots,N_{h},{n = 1},2,\cdots,{N_{h}Q_{h}}} & \lbrack{Equation}\rbrack\end{matrix}$

wherein N_h is the number of antenna ports having the same polarizationin the first dimension and Q_h is an oversampling factor used in thefirst dimension.

Preferably, the second matrix may be composed of one or more columnsselected from a DFT (Discrete Fourier Transform) matrix generatedaccording to the equation below,

$\begin{matrix}{{D_{({mn})}^{N_{v} \times N_{v}Q_{v}} = {\frac{1}{\sqrt{N_{v}}}e^{j\frac{2{\pi {({m - 1})}}{({n - 1})}}{N_{v}Q_{v}}}}},{m = 1},2,\cdots,N_{v},{n = 1},2,\cdots,{N_{v}Q_{v}}} & \lbrack{Equation}\rbrack\end{matrix}$

wherein N_v is the number of antenna ports having the same polarizationin the second dimension and Q_v is an oversampling factor used in thesecond dimension.

Advantageous Effects

According to embodiments of the present invention, it is possible tosmoothly perform transmission and reception of signals (or channels)between a transmitting end and a receiving end by defining a method ofconfiguring a codebook in a wireless communication system supporting2D-AAS based 3D MIMO.

In addition, according to embodiments of the present invention, it ispossible to maximize a beamforming gain in a wireless communicationsystem supporting 2D-AAS based 3D MIMO.

Effects which may be obtained by the present invention are not limitedto the aforementioned effects, and other effects that have not beendescribed may be clearly understood by a person having ordinary skill inthe art to which the present invention pertains from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included herein as a part of thedescription for help understanding the present invention, provideembodiments of the present invention, and describe the technicalfeatures of the present invention with the description below.

FIG. 1 illustrates the structure of a radio frame in a wirelesscommunication system to which the present invention may be applied.

FIG. 2 is a diagram illustrating a resource grid for a downlink slot ina wireless communication system to which the present invention may beapplied.

FIG. 3 illustrates a structure of downlink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 4 illustrates a structure of uplink subframe in a wirelesscommunication system to which the present invention may be applied.

FIG. 5 shows the configuration of a known MIMO communication system.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

FIG. 7 is a diagram for describing a basic concept of a codebook-basedprecoding in a wireless communication system to which the presentinvention may be applied.

FIG. 8 illustrates reference signal patterns mapped to downlink resourceblock pairs in a wireless communication system to which the presentinvention may be applied.

FIG. 9 is a diagram illustrating resources to which reference signalsare mapped in a wireless communication system to which the presentinvention may be applied.

FIG. 10 illustrates a 2D-AAS having 64 antenna elements in a wirelesscommunication system to which the present invention may be applied.

FIG. 11 illustrates a system in which an eNB or UE has a plurality oftransmission/reception antennas capable of forming a 3-Dimension (3D)beam based on the AAS in a wireless communication system to which thepresent invention may be applied.

FIG. 12 illustrates a 2D antenna system having cross-polarizations in awireless communication system to which the present invention may beapplied.

FIG. 13 illustrates a transceiver unit model in a wireless communicationsystem to which the present invention may be applied.

FIG. 14 illustrates a 2D AAS in a wireless communication system to whichthe present invention is applicable.

FIGS. 15 to 44 are diagrams for describing a method of configuring acodebook according to an embodiment of the present invention.

FIG. 45 is a diagram illustrating a method for transmitting andreceiving a codebook-based signal according to an embodiment of thepresent invention.

FIG. 46 is a block diagram of a wireless communication device accordingto an embodiment of the present invention.

MODE FOR INVENTION

Some embodiments of the present invention are described in detail withreference to the accompanying drawings. A detailed description to bedisclosed along with the accompanying drawings are intended to describesome embodiments of the present invention and are not intended todescribe a sole embodiment of the present invention. The followingdetailed description includes more details in order to provide fullunderstanding of the present invention. However, those skilled in theart will understand that the present invention may be implementedwithout such more details.

In some cases, in order to avoid that the concept of the presentinvention becomes vague, known structures and devices are omitted or maybe shown in a block diagram form based on the core functions of eachstructure and device.

In this specification, a base station has the meaning of a terminal nodeof a network over which the base station directly communicates with adevice. In this document, a specific operation that is described to beperformed by a base station may be performed by an upper node of thebase station according to circumstances. That is, it is evident that ina network including a plurality of network nodes including a basestation, various operations performed for communication with a devicemay be performed by the base station or other network nodes other thanthe base station. The base station (BS) may be substituted with anotherterm, such as a fixed station, a Node B, an eNB (evolved-NodeB), a BaseTransceiver System (BTS), or an access point (AP). Furthermore, thedevice may be fixed or may have mobility and may be substituted withanother term, such as User Equipment (UE), a Mobile Station (MS), a UserTerminal (UT), a Mobile Subscriber Station (MSS), a Subscriber Station(SS), an Advanced Mobile Station (AMS), a Wireless Terminal (WT), aMachine-Type Communication (MTC) device, a Machine-to-Machine (M2M)device, or a Device-to-Device (D2D) device.

Hereinafter, downlink (DL) means communication from an eNB to UE, anduplink (UL) means communication from UE to an eNB. In DL, a transmittermay be part of an eNB, and a receiver may be part of UE. In UL, atransmitter may be part of UE, and a receiver may be part of an eNB.

Specific terms used in the following description have been provided tohelp understanding of the present invention, and the use of suchspecific terms may be changed in various forms without departing fromthe technical sprit of the present invention.

The following technologies may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), and Non-OrthogonalMultiple Access (NOMA). CDMA may be implemented using a radiotechnology, such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asGlobal System for Mobile communications (GSM)/General Packet RadioService (GPRS)/Enhanced Data rates for GSM Evolution (EDGE). OFDMA maybe implemented using a radio technology, such as Institute of Electricaland Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is part of a UniversalMobile Telecommunications System (UMTS). 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is part of an Evolved UMTS(E-UMTS) using evolved UMTS Terrestrial Radio Access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-Advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A is chieflydescribed, but the technical characteristics of the present inventionare not limited thereto.

General System to which the Present Invention May be Applied

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

3GPP LTE/LTE-A support a radio frame structure type 1 which may beapplicable to Frequency Division Duplex (FDD) and a radio framestructure which may be applicable to Time Division Duplex (TDD).

The size of a radio frame in the time domain is represented as amultiple of a time unit of T_s=1/(15000*2048). A UL and DL transmissionincludes the radio frame having a duration of T_f=307200*T_s=10 ms.

FIG. 1(a) exemplifies a radio frame structure type 1. The type 1 radioframe may be applied to both of full duplex FDD and half duplex FDD.

A radio frame includes 10 subframes. A radio frame includes 20 slots ofT_slot=15360*T_s=0.5 ms length, and 0 to 19 indexes are given to each ofthe slots. One subframe includes consecutive two slots in the timedomain, and subframe i includes slot 2 i and slot 2 i+1. The timerequired for transmitting a subframe is referred to as a transmissiontime interval (TTI). For example, the length of the subframe i may be 1ms and the length of a slot may be 0.5 ms.

A UL transmission and a DL transmission I the FDD are distinguished inthe frequency domain. Whereas there is no restriction in the full duplexFDD, a UE may not transmit and receive simultaneously in the half duplexFDD operation.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and includes a pluralityof Resource Blocks (RBs) in a frequency domain. In 3GPP LTE, OFDMsymbols are used to represent one symbol period because OFDMA is used indownlink. An OFDM symbol may be called one SC-FDMA symbol or symbolperiod. An RB is a resource allocation unit and includes a plurality ofcontiguous subcarriers in one slot.

FIG. 1(b) shows frame structure type 2.

A type 2 radio frame includes two half frame of 153600*T_s=5 ms lengtheach. Each half frame includes 5 subframes of 30720*T_s=1 ms length.

In the frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether uplink and downlink areallocated (or reserved) to all subframes.

Table 1 shows the uplink-downlink configuration.

TABLE 1 Uplink- Downlink- Downlink to-Uplink config- Switch-pointSubframe number uration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D DD D D 6 5 ms D S U U U D S U U D

Referring to Table 1, in each subframe of the radio frame, ‘D’represents a subframe for a DL transmission, ‘U’ represents a subframefor UL transmission, and ‘S’ represents a special subframe includingthree types of fields including a Downlink Pilot Time Slot (DwPTS), aGuard Period (GP), and a Uplink Pilot Time Slot (UpPTS).

A DwPTS is used for an initial cell search, synchronization or channelestimation in a UE. A UpPTS is used for channel estimation in an eNB andfor synchronizing a UL transmission synchronization of a UE. A GP isduration for removing interference occurred in a UL owing to multi-pathdelay of a DL signal between a UL and a DL.

Each subframe i includes slot 2 i and slot 2 i+1 of T_slot=15360*T_s=0.5ms.

The UL-DL configuration may be classified into 7 types, and the positionand/or the number of a DL subframe, a special subframe and a UL subframeare different for each configuration.

A point of time at which a change is performed from downlink to uplinkor a point of time at which a change is performed from uplink todownlink is called a switching point. The periodicity of the switchingpoint means a cycle in which an uplink subframe and a downlink subframeare changed is identically repeated. Both 5 ms and 10 ms are supportedin the periodicity of a switching point. If the periodicity of aswitching point has a cycle of a 5 ms downlink-uplink switching point,the special subframe S is present in each half frame. If the periodicityof a switching point has a cycle of a 5 ms downlink-uplink switchingpoint, the special subframe S is present in the first half frame only.

In all the configurations, 0 and 5 subframes and a DwPTS are used foronly downlink transmission. An UpPTS and a subframe subsequent to asubframe are always used for uplink transmission.

Such uplink-downlink configurations may be known to both an eNB and UEas system information. An eNB may notify UE of a change of theuplink-downlink allocation state of a radio frame by transmitting onlythe index of uplink-downlink configuration information to the UEwhenever the uplink-downlink configuration information is changed.Furthermore, configuration information is kind of downlink controlinformation and may be transmitted through a Physical Downlink ControlChannel (PDCCH) like other scheduling information. Configurationinformation may be transmitted to all UEs within a cell through abroadcast channel as broadcasting information.

Table 2 represents configuration (length of DwPTS/GP/UpPTS) of a specialsubframe.

TABLE 2 Normal cyclic prefix in Extended cyclic prefix in downlinkdownlink UpPTS UpPTS Normal Extended Normal Extended Special cycliccyclic cyclic cyclic subframe prefix in prefix prefix in prefix inconfiguration DwPTS uplink in uplink DwPTS uplink uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The structure of a radio subframe according to the example of FIG. 1 isjust an example, and the number of subcarriers included in a radioframe, the number of slots included in a subframe and the number of OFDMsymbols included in a slot may be changed in various manners.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

Referring to FIG. 2, one downlink slot includes a plurality of OFDMsymbols in a time domain. It is described herein that one downlink slotincludes 7 OFDMA symbols and one resource block includes 12 subcarriersfor exemplary purposes only, and the present invention is not limitedthereto.

Each element on the resource grid is referred to as a resource element,and one resource block (RB) includes 12×7 resource elements. The numberof RBs NADL included in a downlink slot depends on a downlinktransmission bandwidth.

The structure of an uplink slot may be the same as that of a downlinkslot.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 3, a maximum of three OFDM symbols located in a frontportion of a first slot of a subframe correspond to a control region inwhich control channels are allocated, and the remaining OFDM symbolscorrespond to a data region in which a physical downlink shared channel(PDSCH) is allocated. Downlink control channels used in 3GPP LTEinclude, for example, a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), and a physicalhybrid-ARQ indicator channel (PHICH).

A PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols (i.e., the size ofa control region) which is used to transmit control channels within thesubframe. A PHICH is a response channel for uplink and carries anacknowledgement (ACK)/not-acknowledgement (NACK) signal for a HybridAutomatic Repeat Request (HARQ). Control information transmitted in aPDCCH is called Downlink Control Information (DCI). DCI includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for aspecific UE group.

A PDCCH may carry information about the resource allocation andtransport format of a downlink shared channel (DL-SCH) (this is alsocalled an “downlink grant”), resource allocation information about anuplink shared channel (UL-SCH) (this is also called a “uplink grant”),paging information on a PCH, system information on a DL-SCH, theresource allocation of a higher layer control message, such as a randomaccess response transmitted on a PDSCH, a set of transmission powercontrol commands for individual UE within specific UE group, and theactivation of a Voice over Internet Protocol (VoIP), etc. A plurality ofPDCCHs may be transmitted within the control region, and UE may monitora plurality of PDCCHs. A PDCCH is transmitted on a single ControlChannel Element (CCE) or an aggregation of some contiguous CCEs. A CCEis a logical allocation unit that is used to provide a PDCCH with acoding rate according to the state of a radio channel. A CCE correspondsto a plurality of resource element groups. The format of a PDCCH and thenumber of available bits of a PDCCH are determined by an associationrelationship between the number of CCEs and a coding rate provided byCCEs.

An eNB determines the format of a PDCCH based on DCI to be transmittedto UE and attaches a Cyclic Redundancy Check (CRC) to controlinformation. A unique identifier (a Radio Network Temporary Identifier(RNTI)) is masked to the CRC depending on the owner or use of a PDCCH.If the PDCCH is a PDCCH for specific UE, an identifier unique to the UE,for example, a Cell-RNTI (C-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for a paging message, a paging indication identifier, forexample, a Paging-RNTI (P-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for system information, more specifically, a SystemInformation Block (SIB), a system information identifier, for example, aSystem Information-RNTI (SI-RNTI) may be masked to the CRC. A RandomAccess-RNTI (RA-RNTI) may be masked to the CRC in order to indicate arandom access response which is a response to the transmission of arandom access preamble by UE.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 4, the uplink subframe may be divided into a controlregion and a data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) carrying uplink control information is allocatedto the control region. A physical uplink shared channel (PUSCH) carryinguser data is allocated to the data region. In order to maintain singlecarrier characteristic, one UE does not send a PUCCH and a PUSCH at thesame time.

A Resource Block (RB) pair is allocated to a PUCCH for one UE within asubframe. RBs belonging to an RB pair occupy different subcarriers ineach of 2 slots. This is called that an RB pair allocated to a PUCCH isfrequency-hopped in a slot boundary.

Multi-Input Multi-Output (MIMO)

A MIMO technology does not use single transmission antenna and singlereception antenna that have been commonly used so far, but uses amulti-transmission (Tx) antenna and a multi-reception (Rx) antenna. Inother words, the MIMO technology is a technology for increasing acapacity or enhancing performance using multi-input/output antennas inthe transmission end or reception end of a wireless communicationsystem. Hereinafter, MIMO is called a “multi-input/output antenna.”.

More specifically, the multi-input/output antenna technology does notdepend on a single antenna path in order to receive a single totalmessage and completes total data by collecting a plurality of datapieces received through several antennas. As a result, themulti-input/output antenna technology can increase a data transfer ratewithin a specific system range and can also increase a system rangethrough a specific data transfer rate.

It is expected that an efficient multi-input/output antenna technologywill be used because next-generation mobile communication requires adata transfer rate much higher than that of existing mobilecommunication. In such a situation, the MIMO communication technology isa next-generation mobile communication technology which may be widelyused in mobile communication UE and a relay node and has been in thespotlight as a technology which may overcome a limit to the transferrate of another mobile communication attributable to the expansion ofdata communication.

Meanwhile, the multi-input/output antenna (MIMO) technology of varioustransmission efficiency improvement technologies that are beingdeveloped has been most in the spotlight as a method capable ofsignificantly improving a communication capacity andtransmission/reception performance even without the allocation ofadditional frequencies or a power increase.

FIG. 5 shows the configuration of a known MIMO communication system.

Referring to FIG. 5, if the number of transmission (Tx) antennas isincreased to N_T and the number of reception (Rx) antennas is increasedto N_R at the same time, a theoretical channel transmission capacity isincreased in proportion to the number of antennas, unlike in the casewhere a plurality of antennas is used only in a transmitter or areceiver. Accordingly, a transfer rate can be improved, and frequencyefficiency can be significantly improved. In this case, a transfer rateaccording to an increase of a channel transmission capacity may betheoretically increased by a value obtained by multiplying the followingrate increment R_i by a maximum transfer rate R_o if one antenna isused.

R _(i)=min(N _(T) ,N _(R))  [Equation 1]

That is, in an MIMO communication system using 4 transmission antennasand 4 reception antennas, for example, a quadruple transfer rate can beobtained theoretically compared to a single antenna system.

Such a multi-input/output antenna technology may be divided into aspatial diversity method for increasing transmission reliability usingsymbols passing through various channel paths and a spatial multiplexingmethod for improving a transfer rate by sending a plurality of datasymbols at the same time using a plurality of transmission antennas.Furthermore, active research is being recently carried out on a methodfor properly obtaining the advantages of the two methods by combiningthe two methods.

Each of the methods is described in more detail below.

First, the spatial diversity method includes a space-time blockcode-series method and a space-time Trelis code-series method using adiversity gain and a coding gain at the same time. In general, theTrelis code-series method is better in terms of bit error rateimprovement performance and the degree of a code generation freedom,whereas the space-time block code-series method has low operationalcomplexity. Such a spatial diversity gain may correspond to an amountcorresponding to the product (N_T×_R) of the number of transmissionantennas (N_T) and the number of reception antennas (N_R).

Second, the spatial multiplexing scheme is a method for sendingdifferent data streams in transmission antennas. In this case, in areceiver, mutual interference is generated between data transmitted by atransmitter at the same time. The receiver removes the interferenceusing a proper signal processing scheme and receives the data. A noiseremoval method used in this case may include a Maximum LikelihoodDetection (MLD) receiver, a Zero-Forcing (ZF) receiver, a Minimum MeanSquare Error (MMSE) receiver, Diagonal-Bell Laboratories LayeredSpace-Time (D-BLAST), and Vertical-Bell Laboratories Layered Space-Time(V-BLAST). In particular, if a transmission end can be aware of channelinformation, a Singular Value Decomposition (SVD) method may be used.

Third, there is a method using a combination of a spatial diversity andspatial multiplexing. If only a spatial diversity gain is to beobtained, a performance improvement gain according to an increase of adiversity disparity is gradually saturated. If only a spatialmultiplexing gain is used, transmission reliability in a radio channelis deteriorated. Methods for solving the problems and obtaining the twogains have been researched and may include a double space-time transmitdiversity (double-STTD) method and a space-time bit interleaved codedmodulation (STBICM).

In order to describe a communication method in a multi-input/outputantenna system, such as that described above, in more detail, thecommunication method may be represented as follows through mathematicalmodeling.

First, as shown in FIG. 5, it is assumed that N_T transmission antennasand NR reception antennas are present.

First, a transmission signal is described below. If the N_T transmissionantennas are present as described above, a maximum number of pieces ofinformation which can be transmitted are N_T, which may be representedusing the following vector.

s=[s ₁ ,s ₂ ,Λ,s _(N) _(T) ]^(T)  [Equation 2]

Meanwhile, transmission power may be different in each of pieces oftransmission information s_1, s_2, . . . , s_NT. In this case, if piecesof transmission power are P_1, P_2, . . . , P_NT, transmissioninformation having controlled transmission power may be representedusing the following vector.

ŝ=[ŝ ₁ ,ŝ ₂ ,Λ,ŝ _(N) _(T) ]T=[P ₁ s ₁ ,P ₂ s ₂ ,Λ,P _(N) _(T) s _(N)_(T) ]^(T)  [Equation 3]

Furthermore, transmission information having controlled transmissionpower in the Equation 3 may be represented as follows using the diagonalmatrix P of transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & {0\mspace{31mu}} \\\; & P_{2} & \; & \; \\\; & \; & O & \; \\{0\mspace{14mu}} & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}{s_{1}\mspace{14mu}} \\{s_{2}\mspace{14mu}} \\{M\mspace{11mu}} \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Meanwhile, the information vector having controlled transmission powerin the Equation 4 is multiplied by a weight matrix W, thus forming N_Ttransmission signals x_1, x_2, . . . , x_NT that are actuallytransmitted. In this case, the weight matrix functions to properlydistribute the transmission information to antennas according to atransport channel condition. The following may be represented using thetransmission signals x_1, x_2, . . . , x_NT.

$\begin{matrix}{x = {\quad{\begin{bmatrix}{x_{1}\mspace{14mu}} \\{x_{2}\mspace{14mu}} \\{M\mspace{14mu}} \\{x_{i}\mspace{20mu}} \\{M\mspace{14mu}} \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}{w_{11}\mspace{14mu}} & {w_{12}\mspace{14mu}} & \Lambda & {w_{1N_{T}}\mspace{14mu}} \\{w_{21}\mspace{14mu}} & {w_{22}\mspace{14mu}} & \Lambda & {w_{2N_{T}}\mspace{14mu}} \\{M\mspace{31mu}} & \; & O & \; \\{w_{i\; 1}\mspace{20mu}} & {w_{i\; 2}\mspace{20mu}} & \Lambda & {w_{{iN}_{T}}\mspace{20mu}} \\{M\mspace{31mu}} & \; & O & \; \\w_{N_{T}1} & w_{N_{T}2} & \Lambda & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{{\hat{s}}_{1}\mspace{14mu}} \\{{\hat{s}}_{2}\mspace{14mu}} \\{M\mspace{11mu}} \\{{\hat{s}}_{j}\mspace{14mu}} \\{M\mspace{11mu}} \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In this case, w_ij denotes weight between an i-th transmission antennaand a j-th transmission information, and W is an expression of a matrixof the weight. Such a matrix W is called a weight matrix or precodingmatrix.

Meanwhile, the transmission signal x, such as that described above, maybe considered to be used in a case where a spatial diversity is used anda case where spatial multiplexing is used.

If spatial multiplexing is used, all the elements of the informationvector s have different values because different signals are multiplexedand transmitted. In contrast, if the spatial diversity is used, all theelements of the information vector s have the same value because thesame signals are transmitted through several channel paths.

A method of mixing spatial multiplexing and the spatial diversity may betaken into consideration. In other words, the same signals may betransmitted using the spatial diversity through 3 transmission antennas,for example, and the remaining different signals may be spatiallymultiplexed and transmitted.

If N_R reception antennas are present, the reception signals y_1, y_2, .. . , y_NR of the respective antennas are represented as follows using avector y.

y=[y ₁ ,y ₂ ,Λ,y _(N) _(R) ]^(T)  [Equation 6]

Meanwhile, if channels in a multi-input/output antenna communicationsystem are modeled, the channels may be classified according totransmission/reception antenna indices. A channel passing through areception antenna i from a transmission antenna j is represented ash_ij. In this case, it is to be noted that in order of the index ofh_ij, the index of a reception antenna comes first and the index of atransmission antenna then comes.

Several channels may be grouped and expressed in a vector and matrixform. For example, a vector expression is described below.

FIG. 6 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

As shown in FIG. 6, a channel from a total of N_T transmission antennasto a reception antenna i may be represented as follows.

h _(i) ^(T) =[h _(i1) ,h _(i2) ,Λ,h _(iN) _(T) ]  [Equation 7]

Furthermore, if all channels from the N_T transmission antenna to NRreception antennas are represented through a matrix expression, such asEquation 7, they may be represented as follows.

$\begin{matrix}{H = {\begin{bmatrix}{h_{1}^{T}\mspace{14mu}} \\{h_{2}^{T}\mspace{14mu}} \\{M\mspace{14mu}} \\{h_{i}^{T}\mspace{14mu}} \\{M\mspace{14mu}} \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}{h_{11}\mspace{14mu}} & {h_{12}\mspace{14mu}} & \Lambda & {h_{1N_{T}}\mspace{14mu}} \\{h_{21}\mspace{14mu}} & {h_{22}\mspace{14mu}} & \Lambda & {h_{2N_{T}}\mspace{14mu}} \\{M\mspace{25mu}} & \; & O & \; \\{h_{i\; 1}\mspace{20mu}} & {h_{i\; 2}\mspace{20mu}} & \Lambda & {h_{{iN}_{T}}\mspace{20mu}} \\{M\mspace{25mu}} & \; & O & \; \\h_{N_{R}1} & h_{N_{R}2} & \Lambda & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Meanwhile, Additive White Gaussian Noise (AWGN) is added to an actualchannel after the actual channel experiences the channel matrix H.Accordingly, AWGN n_1, n_2, . . . , n_NR added to the N_R receptionantennas, respectively, are represented using a vector as follows.

n=[n ₁ ,n ₂ ,Λ,n _(N) _(R) ]^(T)  [Equation 9]

A transmission signal, a reception signal, a channel, and AWGN in amulti-input/output antenna communication system may be represented tohave the following relationship through the modeling of the transmissionsignal, reception signal, channel, and AWGN, such as those describedabove.

$\begin{matrix}{y = {\quad{\begin{bmatrix}{y_{1}\mspace{14mu}} \\{y_{2}\mspace{14mu}} \\{M\mspace{14mu}} \\{y_{i}\mspace{20mu}} \\{M\mspace{14mu}} \\y_{N_{T}}\end{bmatrix} = {{{\begin{bmatrix}{h_{11}\mspace{14mu}} & {h_{12}\mspace{14mu}} & \Lambda & {h_{1N_{T}}\mspace{14mu}} \\{h_{21}\mspace{14mu}} & {h_{22}\mspace{14mu}} & \Lambda & {h_{2N_{T}}\mspace{14mu}} \\{M\mspace{31mu}} & \; & O & \; \\{h_{i\; 1}\mspace{20mu}} & {h_{i\; 2}\mspace{20mu}} & \Lambda & {h_{{iN}_{T}}\mspace{20mu}} \\{M\mspace{31mu}} & \; & O & \; \\h_{N_{R}1} & h_{N_{R}2} & \Lambda & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}{x_{1}\mspace{14mu}} \\{x_{2}\mspace{14mu}} \\{M\mspace{14mu}} \\{x_{j}\mspace{14mu}} \\{M\mspace{14mu}} \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}{n_{1}\mspace{14mu}} \\{n_{2}\mspace{14mu}} \\{M\mspace{14mu}} \\{n_{i}\mspace{20mu}} \\{M\mspace{14mu}} \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Meanwhile, the number of rows and columns of the channel matrix Hindicative of the state of channels is determined by the number oftransmission/reception antennas. In the channel matrix H, as describedabove, the number of rows becomes equal to the number of receptionantennas N_R, and the number of columns becomes equal to the number oftransmission antennas N_T. That is, the channel matrix H becomes anN_R×N_T matrix.

In general, the rank of a matrix is defined as a minimum number of thenumber of independent rows or columns. Accordingly, the rank of thematrix is not greater than the number of rows or columns. As for figuralstyle, for example, the rank H of the channel matrix H is limited asfollows.

rank(H)≤min(N _(T) ,N _(R))  [Equation 11]

Furthermore, if a matrix is subjected to Eigen value decomposition, arank may be defined as the number of Eigen values that belong to Eigenvalues and that are not 0. Likewise, if a rank is subjected to SingularValue Decomposition (SVD), it may be defined as the number of singularvalues other than 0. Accordingly, the physical meaning of a rank in achannel matrix may be said to be a maximum number on which differentinformation may be transmitted in a given channel.

In this specification, a “rank” for MIMO transmission indicates thenumber of paths through which signals may be independently transmittedat a specific point of time and a specific frequency resource. The“number of layers” indicates the number of signal streams transmittedthrough each path. In general, a rank has the same meaning as the numberof layers unless otherwise described because a transmission end sendsthe number of layers corresponding to the number of ranks used in signaltransmission.

Hereinafter, in relation to the MIMO transport techniques describedabove, a codebook-based precoding technique will be described in detail.

FIG. 7 is a diagram for describing a basic concept of a codebook-basedprecoding in a wireless communication system to which the presentinvention may be applied.

According to the codebook-based precoding technique, a transmitting-endand a receiving end share codebook information that includes apredetermined number of precoding matrixes according to a transmissionrank, the number of antennas, and so on.

That is, in the case that feedback information is finite, theprecoding-based codebook technique may be used.

A receiving-end may measure a channel state through a receiving signal,and may feedback a finite number of preferred matrix information (i.e.,index of the corresponding precoding matrix) based on the codebookinformation described above. For example, a receiving-end may measure asignal in Maximum Likelihood (ML) or Minimum Mean Square Error (MMSE)technique, and may select an optimal precoding matrix.

FIG. 7 shows that a receiving-end transmits the precoding matrixinformation for each codeword to a transmitting-end, but the presentinvention is not limited thereto.

The transmitting-end that receives the feedback information from thereceiving-end may select a specific precoding matrix from the codebookbased on the received information. The transmitting-end that selects theprecoding matrix may perform precoding in a manner of multiplying layersignals, of which number amounts to a transmission rank, by the selectedprecoding matrix and may transmit the precoded transmission signal via aplurality of antennas. The number of rows in a precoding matrix is equalto the number of antennas, while the number of columns is equal to arank value. Since the rank value is equal to the number of layers, thenumber of the columns is equal to the number of the layers. Forinstance, when the number of transmitting antennas and the number oflayers are 4 and 2, respectively, a precoding matrix may include 4×2matrix. Equation 12 below represents an operation of mapping informationmapped to each layer to a respective antenna through the precodingmatrix in the case.

$\begin{matrix}{\begin{bmatrix}y_{1} \\y_{2} \\y_{3} \\y_{4}\end{bmatrix} = {\begin{bmatrix}p_{11} & y_{1} \\p_{12} & y_{1} \\p_{13} & y_{1} \\p_{14} & y_{1}\end{bmatrix} \cdot \begin{bmatrix}x_{1} \\x_{2}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

Referring to Equation 12, information mapped to a layer includes x_1 andx_2 and each element p_ij of 4×2 matrix is a weight used for precoding.y_1, y_2, y_3 and y_4 indicate information mapped to antennas and may betransmitted via corresponding antennas by OFDM transmission schemes,respectively.

The receiving-end that receives the signal precoded and transmitted inthe transmitting-end may reconstruct the received signal by performinginverse processing of the precoding performed in the transmitting-end.Generally, since a precoding matrix satisfies such a unitary matrix (U)condition as ‘U*ÛH=I’ (herein, ÛH means an Hermit matrix of matrix U),the above-mentioned inverse processing of the precoding may be performedin a manner of multiplying the received signal by Hermit matrix PH ofthe precoding matrix P used for the precoding performed by thetransmitting-end.

In addition, since the precoding is requested to have good performancefor antenna configurations of various types, it may be necessary toconsider performance for various antenna configurations in codebookdesign. In the following description, an exemplary configuration ofmultiple antennas is explained.

In the conventional 3GPP LTE system (e.g., system according to 3GPP LTERelease-8 or Release-9 Standard), since maximum four transmissionantennas are supported in DL, a codebook for four transmission antennasis designed. In the 3GPP LTE-A system evolved from the conventional 3GPPLTE system, maximum eight transmission antennas may be supported in DL.Accordingly, it may be necessary to design a precoding codebook thatprovides good performance for a DL transmission via maximum eighttransmission antennas.

Moreover, when a codebook is designed, generally required are constantmodulus property, finite alphabet, restriction on a codebook size,nested property, and providing good performance for various antennaconfigurations.

The constant modulus property means a property that amplitude of eachchannel component of a precoding matrix configuring a codebook isconstant. According to this property, no matter what kind of a precodingmatrix is used, power levels transmitted from all antennas may bemaintained equal to each other. Hence, it may be able to raiseefficiency in using a power amplifier.

The finite alphabet means to configure precoding matrixes usingquadrature phase shift keying (QPSK) alphabet (i.e., ±1, ±j) only excepta scaling factor in the case of two transmitting antennas, for example.Accordingly, when multiplication is performed on a precoding matrix by aprecoder, it may alleviate the complexity of calculation.

The codebook size may be restricted as a predetermined size or smaller.Since a size of a codebook increases, precoding matrixes for variouscases may be included in the codebook, and accordingly, a channel statusmay be more accurately reflected. However, the number of bits of aprecoding matrix indicator (PMI) correspondingly increases to causesignaling overhead.

The nested property means that a portion of a high rank precoding matrixis configured with a low rank precoding matrix. Thus, when thecorresponding precoding matrix is configured, an appropriate performancemay be guaranteed even in the case that a BS determines to perform a DLtransmission of a transmission rank lower than a channel rank indicatedby a rank indicator (RI) reported from a UE. In addition, according tothis property, complexity of channel quality information (CQI)calculation may be reduced. This is because calculation for a precodingmatrix selection may be shared in part when an operation of selecting aprecoding matrix from precoding matrixes designed for different ranks isperformed.

Providing good performance for various antenna configurations may meanthat providing performance over a predetermined level is required forvarious cases including a low correlated antenna configuration, a highcorrelated antenna configuration, a cross-polarized antennaconfiguration and the like.

Reference Signal (RS)

In a wireless communication system, a signal may be distorted duringtransmission because data is transmitted through a radio channel. Inorder for a reception end to accurately receive a distorted signal, thedistortion of a received signal needs to be corrected using channelinformation. In order to detect channel information, a method ofdetecting channel information using the degree of the distortion of asignal transmission method and a signal known to both the transmissionside and the reception side when they are transmitted through a channelis chiefly used. The aforementioned signal is called a pilot signal orreference signal (RS).

Furthermore recently, when most of mobile communication systems transmita packet, they use a method capable of improving transmission/receptiondata efficiency by adopting multiple transmission antennas and multiplereception antennas instead of using one transmission antenna and onereception antenna used so far. When data is transmitted and receivedusing multiple input/output antennas, a channel state between thetransmission antenna and the reception antenna must be detected in orderto accurately receive the signal. Accordingly, each transmission antennamust have an individual reference signal.

In a mobile communication system, an RS may be basically divided intotwo types depending on its object. There are an RS having an object ofobtaining channel state information and an RS used for datademodulation. The former has an object of obtaining, by a UE, to obtainchannel state information in the downlink. Accordingly, a correspondingRS must be transmitted in a wideband, and a UE must be capable ofreceiving and measuring the RS although the UE does not receive downlinkdata in a specific subframe. Furthermore, the former is also used forradio resources management (RRM) measurement, such as handover. Thelatter is an RS transmitted along with corresponding resources when aneNB transmits the downlink. A UE may perform channel estimation byreceiving a corresponding RS and thus may demodulate data. Thecorresponding RS must be transmitted in a region in which data istransmitted.

A downlink RS includes one common RS (CRS) for the acquisition ofinformation about a channel state shared by all of UEs within a cell andmeasurement, such as handover, and a dedicated RS (DRS) used for datademodulation for only a specific UE. Information for demodulation andchannel measurement can be provided using such RSs. That is, the DRS isused for only data demodulation, and the CRS is used for the two objectsof channel information acquisition and data demodulation.

The reception side (i.e., UE) measures a channel state based on a CRSand feeds an indicator related to channel quality, such as a channelquality indicator (Cal), a precoding matrix index (PMI) and/or a rankindicator (RI), back to the transmission side (i.e., an eNB). The CRS isalso called a cell-specific RS. In contrast, a reference signal relatedto the feedback of channel state information (CSI) may be defined as aCSI-RS.

The DRS may be transmitted through resource elements if data on a PDSCHneeds to be demodulated. A UE may receive information about whether aDRS is present through a higher layer, and the DRS is valid only if acorresponding PDSCH has been mapped. The DRS may also be called aUE-specific RS or demodulation RS (DMRS).

FIG. 8 illustrates reference signal patterns mapped to downlink resourceblock pairs in a wireless communication system to which the presentinvention may be applied.

Referring to FIG. 8, a downlink resource block pair, that is, a unit inwhich a reference signal is mapped, may be represented in the form ofone subframe in a time domain X 12 subcarriers in a frequency domain.That is, in a time axis (an x axis), one resource block pair has alength of 14 OFDM symbols in the case of a normal cyclic prefix (CP)(FIG. 8a ) and has a length of 12 OFDM symbols in the case of anextended cyclic prefix (CP) (FIG. 8b ). In the resource block lattice,resource elements (REs) indicated by “0”, “1”, “2”, and “3” mean thelocations of the CRSs of antenna port indices “0”, “1”, “2”, and “3”,respectively, and REs indicated by “D” mean the location of a DRS.

A CRS is described in more detail below. The CRS is a reference signalwhich is used to estimate the channel of a physical antenna and may bereceived by all UEs located within a cell in common. The CRS isdistributed to a full frequency bandwidth. That is, the CRS iscell-specific signal and is transmitted every subframe in a wideband.Furthermore, the CRS may be used for channel quality information (CSI)and data demodulation.

A CRS is defined in various formats depending on an antenna array on thetransmitting side (eNB). In the 3GPP LTE system (e.g., Release-8), an RSfor a maximum four antenna ports is transmitted depending on the numberof transmission antennas of an eNB. The side from which a downlinksignal is transmitted has three types of antenna arrays, such as asingle transmission antenna, two transmission antennas and fourtransmission antennas. For example, if the number of transmissionantennas of an eNB is two, CRSs for a No. 0 antenna port and a No. 1antenna port are transmitted. If the number of transmission antennas ofan eNB is four, CRSs for No. 0-No. 3 antenna ports are transmitted. Ifthe number of transmission antennas of an eNB is four, a CRS pattern inone RB is shown in FIG. 8.

If an eNB uses a single transmission antenna, reference signals for asingle antenna port are arrayed.

If an eNB uses two transmission antennas, reference signals for twotransmission antenna ports are arrayed using a time divisionmultiplexing (TDM) scheme and/or a frequency division multiplexing (FDM)scheme. That is, different time resources and/or different frequencyresources are allocated in order to distinguish between referencesignals for two antenna ports.

Furthermore, if an eNB uses four transmission antennas, referencesignals for four transmission antenna ports are arrayed using the TDMand/or FDM schemes. Channel information measured by the reception side(i.e., UE) of a downlink signal may be used to demodulate datatransmitted using a transmission scheme, such as single transmissionantenna transmission, transmission diversity, closed-loop spatialmultiplexing, open-loop spatial multiplexing or amulti-user-multi-input/output (MIMO) antenna.

If a multi-input multi-output antenna is supported, when a RS istransmitted by a specific antenna port, the RS is transmitted in thelocations of resource elements specified depending on a pattern of theRS and is not transmitted in the locations of resource elementsspecified for other antenna ports. That is, RSs between differentantennas do not overlap.

A DRS is described in more detail below. The DRS is used to demodulatedata. In multi-input multi-output antenna transmission, precoding weightused for a specific UE is combined with a transmission channeltransmitted by each transmission antenna when the UE receives an RS, andis used to estimate a corresponding channel without any change.

A 3GPP LTE system (e.g., Release-8) supports a maximum of fourtransmission antennas, and a DRS for rank 1 beamforming is defined. TheDRS for rank 1 beamforming also indicates an RS for an antenna portindex 5.

In an LTE-A system, that is, an advanced and developed form of the LTEsystem, the design is necessary to support a maximum of eighttransmission antennas in the downlink of an eNB. Accordingly, RSs forthe maximum of eight transmission antennas must be also supported. Inthe LTE system, only downlink RSs for a maximum of four antenna portshas been defined. Accordingly, if an eNB has four to a maximum of eightdownlink transmission antennas in the LTE-A system, RSs for theseantenna ports must be additionally defined and designed. Regarding theRSs for the maximum of eight transmission antenna ports, theaforementioned RS for channel measurement and the aforementioned RS fordata demodulation must be designed.

One of important factors that must be considered in designing an LTE-Asystem is backward compatibility, that is, that an LTE UE must welloperate even in the LTE-A system, which must be supported by the system.From an RS transmission viewpoint, in the time-frequency domain in whicha CRS defined in LTE is transmitted in a full band every subframe, RSsfor a maximum of eight transmission antenna ports must be additionallydefined. In the LTE-A system, if an RS pattern for a maximum of eighttransmission antennas is added in a full band every subframe using thesame method as the CRS of the existing LTE, RS overhead is excessivelyincreased.

Accordingly, the RS newly designed in the LTE-A system is basicallydivided into two types, which include an RS having a channel measurementobject for the selection of MCS or a PMI (channel state information-RSor channel state indication-RS (CSI-RS)) and an RS for the demodulationof data transmitted through eight transmission antennas (datademodulation-RS (DM-RS)).

The CSI-RS for the channel measurement object is characterized in thatit is designed for an object focused on channel measurement unlike theexisting CRS used for objects for measurement, such as channelmeasurement and handover, and for data demodulation. Furthermore, theCSI-RS may also be used for an object for measurement, such as handover.The CSI-RS does not need to be transmitted every subframe unlike the CRSbecause it is transmitted for an object of obtaining information about achannel state. In order to reduce overhead of a CSI-RS, the CSI-RS isintermittently transmitted on the time axis.

For data demodulation, a DM-RS is dedicatedly transmitted to a UEscheduled in a corresponding time-frequency domain. That is, a DM-RS fora specific UE is transmitted only in a region in which the correspondingUE has been scheduled, that is, in the time-frequency domain in whichdata is received.

In the LTE-A system, a maximum of eight transmission antennas aresupported in the downlink of an eNB. In the LTE-A system, if RSs for amaximum of eight transmission antennas are transmitted in a full bandevery subframe using the same method as the CRS in the existing LTE, RSoverhead is excessively increased. Accordingly, in the LTE-A system, anRS has been separated into the CSI-RS of the CSI measurement object forthe selection of MCS or a PMI and the DM-RS for data demodulation, andthus the two RSs have been added. The CSI-RS may also be used for anobject, such as RRM measurement, but has been designed for a main objectfor the acquisition of CSI. The CSI-RS does not need to be transmittedevery subframe because it is not used for data demodulation.Accordingly, in order to reduce overhead of the CSI-RS, the CSI-RS isintermittently transmitted on the time axis. That is, the CSI-RS has aperiod corresponding to a multiple of the integer of one subframe andmay be periodically transmitted or transmitted in a specifictransmission pattern. In this case, the period or pattern in which theCSI-RS is transmitted may be set by an eNB.

For data demodulation, a DM-RS is dedicatedly transmitted to a UEscheduled in a corresponding time-frequency domain. That is, a DM-RS fora specific UE is transmitted only in the region in which scheduling isperformed for the corresponding UE, that is, only in the time-frequencydomain in which data is received.

In order to measure a CSI-RS, a UE must be aware of information aboutthe transmission subframe index of the CSI-RS for each CSI-RS antennaport of a cell to which the UE belongs, the location of a CSI-RSresource element (RE) time-frequency within a transmission subframe, anda CSI-RS sequence.

In the LTE-A system, an eNB has to transmit a CSI-RS for each of amaximum of eight antenna ports. Resources used for the CSI-RStransmission of different antenna ports must be orthogonal. When one eNBtransmits CSI-RSs for different antenna ports, it may orthogonallyallocate the resources according to the FDM/TDM scheme by mapping theCSI-RSs for the respective antenna ports to different REs.Alternatively, the CSI-RSs for different antenna ports may betransmitted according to the CDM scheme for mapping the CSI-RSs topieces of code orthogonal to each other.

When an eNB notifies a UE belonging to the eNB of information on aCSI-RS, first, the eNB must notify the UE of information about atime-frequency in which a CSI-RS for each antenna port is mapped.Specifically, the information includes subframe numbers in which theCSI-RS is transmitted or a period in which the CSI-RS is transmitted, asubframe offset in which the CSI-RS is transmitted, an OFDM symbolnumber in which the CSI-RS RE of a specific antenna is transmitted,frequency spacing, and the offset or shift value of an RE in thefrequency axis.

A CSI-RS is transmitted through one, two, four or eight antenna ports.Antenna ports used in this case are p=15, p=15, 16, p=15, . . . , 18,and p=15, . . . , 22, respectively. A CSI-RS may be defined for only asubcarrier spacing Δf=15 kHz.

In a subframe configured for CSI-RS transmission, a CSI-RS sequence ismapped to a complex-valued modulation symbol a_k,l̂(p) used as areference symbol on each antenna port p as in Equation 13.

$\begin{matrix}{{a_{k,l}^{(p)} = {w_{l^{''}} \cdot {r_{l,n_{s}}\left( m^{\prime} \right)}}}{k = {k^{\prime} + {12m} + \left\{ {{\begin{matrix}{- 0} & {{{{{for}\mspace{14mu} p} \in \left\{ {15,16} \right\}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\mspace{20mu}} \\{- 6} & {{{{{for}\mspace{14mu} p} \in \left\{ {17,18} \right\}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\mspace{20mu}} \\{- 1} & {{{{{for}\mspace{14mu} p} \in \left\{ {19,20} \right\}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\mspace{20mu}} \\{- 7} & {{{{{for}\mspace{14mu} p} \in \left\{ {21,22} \right\}},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\mspace{20mu}} \\{- 0} & {{{{for}\mspace{14mu} p} \in \left\{ {15,16} \right\}},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 3} & {{{{for}\mspace{14mu} p} \in \left\{ {17,18} \right\}},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \left\{ {19,20} \right\}},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}} \\{- 9} & {{{{for}\mspace{14mu} p} \in \left\{ {21,22} \right\}},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\end{matrix}l} = {l^{\prime} + \left\{ {{\begin{matrix}{l^{''}\mspace{11mu}} & {{{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 0\text{-}19},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\mspace{20mu}} \\{2l^{''}} & {{{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 20\text{-}31},{{normal}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\;} \\{l^{''}\mspace{11mu}} & {{{CSI}\mspace{14mu} {reference}\mspace{14mu} {signal}\mspace{14mu} {configurations}\mspace{14mu} 0\text{-}27},{{extended}\mspace{14mu} {cyclic}\mspace{14mu} {prefix}}}\end{matrix}w_{l^{''}}} = \left\{ {{{\begin{matrix}1 & {p \in \left\{ {15,17,19,21} \right\}} \\\left( {- 1} \right)^{l^{''}} & {p \in \left\{ {16,18,20,22} \right\}}\end{matrix}l^{''}} = 0},{{1m} = 0},1,\ldots,{{N_{RB}^{DL} - {1m^{\prime}}} = {m + \left\lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \right\rfloor}}} \right.} \right.}} \right.}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

In Equation 13, (k′,l′) (wherein k′ is a subcarrier index within aresource block and l′ indicates an OFDM symbol index within a slot.) andthe condition of n_s is determined depending on a CSI-RS configuration,such as Table 3 or Table 4.

Table 3 illustrates the mapping of (k′,l′) from a CSI-RS configurationin a normal CP.

TABLE 3 CSI reference Number of CSI reference signals configured signal1 or 2 4 8 configuration (k′, l′) n_(s) mod 2 (k′, l′) n_(s) mod 2 (k′,l′) n_(s) mod 2 Frame structure 0 (9, 5) 0 (9, 5) 0 (9, 5) 0 type 1 1(11, 2)  1 (11, 2)  1 (11, 2)  1 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 3 (7, 2) 1(7, 2) 1 (7, 2) 1 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 0 6(10, 2)  1 (10, 2)  1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5) 1(8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15(2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame structure20 (11, 1)  1 (11, 1)  1 (11, 1)  1 type 2 only 21 (9, 1) 1 (9, 1) 1(9, 1) 1 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 23 (10, 1)  1 (10, 1)  1 24(8, 1) 1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1)1 29 (2, 1) 1 30 (1, 1) 1 31 (0, 1) 1

Table 4 illustrates the mapping of (k′,l′) from a CSI-RS configurationin an extended CP.

TABLE 4 CSI reference Number of CSI reference signals configured signal1 or 2 4 8 configuration (k′, l′) n_(s) mod 2 (k′, l′) n_(s) mod 2 (k′,l′) n_(s) mod 2 Frame structure 0 (11, 4)  0 (11, 4)  0 (11, 4) 0 type 1and 2 1 (9, 4) 0 (9, 4) 0  (9, 4) 0 2 (10, 4)  1 (10, 4)  1 (10, 4) 1 3(9, 4) 1 (9, 4) 1  (9, 4) 1 4 (5, 4) 0 (5, 4) 0 5 (3, 4) 0 (3, 4) 0 6(4, 4) 1 (4, 4) 1 7 (3, 4) 1 (3, 4) 1 8 (8, 4) 0 9 (6, 4) 0 10 (2, 4) 011 (0, 4) 0 12 (7, 4) 1 13 (6, 4) 1 14 (1, 4) 1 15 (0, 4) 1 Framestructure 16 (11, 1)  1 (11, 1)  1 (11, 1) 1 type 2 only 17 (10, 1)  1(10, 1)  1 (10, 1) 1 18 (9, 1) 1 (9, 1) 1  (9, 1) 1 19 (5, 1) 1 (5, 1) 120 (4, 1) 1 (4, 1) 1 21 (3, 1) 1 (3, 1) 1 22 (8, 1) 1 23 (7, 1) 1 24(6, 1) 1 25 (2, 1) 1 26 (1, 1) 1 27 (0, 1) 1

Referring to Table 3 and Table 4, in the transmission of a CSI-RS, inorder to reduce inter-cell interference (ICI) in a multi-cellenvironment including a heterogeneous network (HetNet) environment, amaximum of 32 different configurations (in the case of a normal CP) or amaximum of 28 different configurations (in the case of an extended CP)are defined.

The CSI-RS configuration is different depending on the number of antennaports and a CP within a cell, and a neighboring cell may have a maximumof different configurations. Furthermore, the CSI-RS configuration maybe divided into a case where it is applied to both an FDD frame and aTDD frame and a case where it is applied to only a TDD frame dependingon a frame structure.

(k′,l′) and n_s are determined depending on a CSI-RS configuration basedon Table 3 and Table 4, and time-frequency resources used for CSI-RStransmission are determined depending on each CSI-RS antenna port.

FIG. 9 is a diagram illustrating resources to which reference signalsare mapped in a wireless communication system to which the presentinvention may be applied.

FIG. 9(a) shows twenty types of CSI-RS configurations available forCSI-RS transmission by one or two CSI-RS antenna ports, FIG. 9(b) showsten types of CSI-RS configurations available for four CSI-RS antennaports, and FIG. 9(c) shows five types of CSI-RS configurations availablefor eight CSI-RS antenna ports.

As described above, radio resources (i.e., an RE pair) in which a CSI-RSis transmitted are determined depending on each CSI-RS configuration.

If one or two antenna ports are configured for CSI-RS transmission withrespect to a specific cell, the CSI-RS is transmitted on radio resourceson a configured CSI-RS configuration of the twenty types of CSI-RSconfigurations shown in FIG. 9(a).

Likewise, when four antenna ports are configured for CSI-RS transmissionwith respect to a specific cell, a CSI-RS is transmitted on radioresources on a configured CSI-RS configuration of the ten types ofCSI-RS configurations shown in FIG. 9(b). Furthermore, when eightantenna ports are configured for CSI-RS transmission with respect to aspecific cell, a CSI-RS is transmitted on radio resources on aconfigured CSI-RS configuration of the five types of CSI-RSconfigurations shown in FIG. 9(c).

A CSI-RS for each antenna port is subjected to CDM for every two antennaports (i.e., {15,16}, {17,18}, {19,20} and {21,22}) on the same radioresources and transmitted. For example, in the case of antenna ports 15and 16, CSI-RS complex symbols for the respective antenna ports 15 and16 are the same, but are multiplied by different types of orthogonalcode (e.g., Walsh code) and mapped to the same radio resources. Thecomplex symbol of the CSI-RS for the antenna port 15 is multiplied by[1, 1], and the complex symbol of the CSI-RS for the antenna port 16 ismultiplied by [1 −1] and mapped to the same radio resources. The same istrue of the antenna ports {17,18}, {19,20} and {21,22}.

A UE may detect a CSI-RS for a specific antenna port by multiplying codeby which a transmitted symbol has been multiplied. That is, atransmitted symbol is multiplied by the code [1 1] multiplied in orderto detect the CSI-RS for the antenna port 15, and a transmitted symbolis multiplied by the code [1 −1] multiplied in order to detect theCSI-RS for the antenna port 16.

Referring to FIGS. 9(a) to 9(c), in the case of the same CSI-RSconfiguration index, radio resources according to a CSI-RS configurationhaving a large number of antenna ports include radio resources having asmall number of CSI-RS antenna ports. For example, in the case of aCSI-RS configuration 0, radio resources for the number of eight antennaports include both radio resources for the number of four antenna portsand radio resources for the number of one or two antenna ports.

A plurality of CSI-RS configurations may be used in one cell. 0 or oneCSI-RS configuration may be used for a non-zero power (NZP) CSI-RS, and0 or several CSI-RS configurations may be used for a zero power (ZP)CSI-RS.

For each bit set to 1 in a zeropower (ZP) CSI-RS (‘ZeroPowerCSI-RS) thatis a bitmap of 16 bits configured by a high layer, a UE assumes zerotransmission power in REs (except a case where an RE overlaps an REassuming a NZP CSI-RS configured by a high layer) corresponding to thefour CSI-RS columns of Table 3 and Table 4. The most significant bit(MSB) corresponds to the lowest CSI-RS configuration index, and nextbits in the bitmap sequentially correspond to next CSI-RS configurationindices.

A CSI-RS is transmitted only in a downlink slot that satisfies thecondition of (n_s mod 2) in Table 3 and Table 4 and a subframe thatsatisfies the CSI-RS subframe configurations.

In the case of the frame structure type 2 (TDD), a CSI-RS is nottransmitted in a special subframe, a synchronization signal (SS), asubframe colliding against a PBCH or SystemInformationBlockType1 (SIB 1)Message transmission or a subframe configured to paging messagetransmission.

Furthermore, an RE in which a CSI-RS for any antenna port belonging toan antenna port set S (S={15}, S={15,16}, S={17,18}, S={19,20} orS={21,22}) is transmitted is not used for the transmission of a PDSCH orfor the CSI-RS transmission of another antenna port.

Time-frequency resources used for CSI-RS transmission cannot be used fordata transmission. Accordingly, data throughput is reduced as CSI-RSoverhead is increased. By considering this, a CSI-RS is not configuredto be transmitted every subframe, but is configured to be transmitted ineach transmission period corresponding to a plurality of subframes. Inthis case, CSI-RS transmission overhead can be significantly reducedcompared to a case where a CSI-RS is transmitted every subframe.

A subframe period (hereinafter referred to as a “CSI transmissionperiod”) T CSI-RS and a subframe offset Δ_CSI-RS for CSI-RS transmissionare shown in Table 5.

Table 5 illustrates CSI-RS subframe configurations.

TABLE 5 CSI-RS periodicity CSI-RS subframe offset CSI-RS-SubframeConfigT_(CSI-RS) Δ_(CSI-RS) I_(CSI-RS) (subframes) (subframes) 0-4 5I_(CSI-RS)  5-14 10 I_(CSI-RS) − 5  15-34 20 I_(CSI-RS) − 15 35-74 40I_(CSI-RS) − 35  75-154 80 I_(CSI-RS) − 75

Referring to Table 5, the CSI-RS transmission period T_CSI-RS and thesubframe offset Δ_CSI-RS are determined depending on the CSI-RS subframeconfiguration I_CSI-RS.

The CSI-RS subframe configuration of Table 5 may be configured as one ofthe aforementioned ‘SubframeConfig’ field and‘zeroTxPowerSubframeConfig’ field. The CSI-RS subframe configuration maybe separately configured with respect to an NZP CSI-RS and a ZP CSI-RS.

A subframe including a CSI-RS satisfies Equation 14.

(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=0  [Equation 14]

In Equation 14, T_CSI-RS means a CSI-RS transmission period, CSI-RSmeans a subframe offset value, n_f means a system frame number, and n_smeans a slot number.

In the case of a UE in which the transmission mode 9 has been configuredwith respect to a serving cell, one CSI-RS resource configuration may beconfigured for the UE. In the case of a UE in which the transmissionmode 10 has been configured with respect to a serving cell, one or moreCSI-RS resource configuration (s) may be configured for the UE.

In the current LTE standard, a CSI-RS configuration includes an antennaport number (antennaPortsCount), a subframe configuration(subframeConfig), and a resource configuration (resourceConfig).Accordingly, the a CSI-RS configuration provides notification that aCSI-RS is transmitted how many antenna port, provides notification ofthe period and offset of a subframe in which a CSI-RS will betransmitted, and provides notification that a CSI-RS is transmitted inwhich RE location (i.e., a frequency and OFDM symbol index) in acorresponding subframe.

Specifically, the following parameters for each CSI-RS (resource)configuration are configured through high layer signaling.

-   -   If the transmission mode 10 has been configured, a CSI-RS        resource configuration identifier    -   A CSI-RS port number (antennaPortsCount): a parameter (e.g., one        CSI-RS port, two CSI-RS ports, four CSI-RS ports or eight CSI-RS        ports) indicative of the number of antenna ports used for CSI-RS        transmission    -   A CSI-RS configuration (resourceConfig) (refer to Table 3 and        Table 4): a parameter regarding a CSI-RS allocation resource        location    -   A CSI-RS subframe configuration (subframeConfig, that is,        I_CSI-RS) (refer to Table 5): a parameter regarding the period        and/or offset of a subframe in which a CSI-RS will be        transmitted    -   If the transmission mode 9 has been configured, transmission        power P_C for CSI feedback: in relation to the assumption of a        UE for reference PDSCH transmission power for feedback, when the        UE derives CSI feedback and takes a value within a [−8, 15] dB        range in a 1-dB step size, P_C is assumed to be the ratio of        energy per resource element (EPRE) per PDSCH RE and a CSI-RS        EPRE.    -   If the transmission mode 10 has been configured, transmission        power P_C for CSI feedback with respect to each CSI process. If        CSI subframe sets C_CSI,0 and C_CSI,1 are configured by a high        layer with respect to a CSI process, P_C is configured for each        CSI subframe set in the CSI process.    -   A pseudo-random sequence generator parameter n_ID    -   If the transmission mode 10 has been configured, a high layer        parameter ‘qcl-CRS-Info-r11’ including a QCL scrambling        identifier for a quasico-located (QCL) type B UE assumption        (qcl-ScramblingIdentity-r11), a CRS port count        (crs-PortsCount-r11), and an MBSFN subframe configuration list        (mbsfn-SubframeConfigList-r11) parameter.

When a CSI feedback value derived by a UE has a value within the [−8,15] dB range, P_C is assumed to be the ration of PDSCH EPRE to CSI-RSEPRE. In this case, the PDSCH EPRE corresponds to a symbol in which theratio of PDSCH EPRE to CRS EPRE is ρ_A.

A CSI-RS and a PMCH are not configured in the same subframe of a servingcell at the same time.

In the frame structure type 2, if four CRS antenna ports have beenconfigured, a CSI-RS configuration index belonging to the [20-31] set(refer to Table 3) in the case of a normal CP or a CSI-RS configurationindex belonging to the [16-27] set (refer to Table 4) in the case of anextended CP is not configured in a UE.

A UE may assume that the CSI-RS antenna port of a CSI-RS resourceconfiguration has a QCL relation with delay spread, Doppler spread,Doppler shift, an average gain and average delay.

A UE in which the transmission mode 10 and the QCL type B have beenconfigured may assume that antenna ports 0-3 corresponding to a CSI-RSresource configuration and antenna ports 15-22 corresponding to a CSI-RSresource configuration have QCL relation with Doppler spread and Dopplershift.

In the case of a UE in which the transmission modes 1-9 have beenconfigured, one ZP CSI-RS resource configuration may be configured inthe UE with respect to a serving cell. In the case of a UE in which thetransmission mode 10 has been configured, one or more ZP CSI-RS resourceconfigurations may be configured in the UE with respect to a servingcell.

The following parameters for a ZP CSI-RS resource configuration may beconfigured through high layer signaling.

-   -   The ZP CSI-RS configuration list (zeroTxPowerResourceConfigList)        (refer to Table 3 and Table 4): a parameter regarding a        zero-power CSI-RS configuration    -   The ZP CSI-RS subframe configuration (eroTxPowerSubframeConfig,        that is, I_CSI-RS) (refer to Table 5): a parameter regarding the        period and/or offset of a subframe in which a zero-power CSI-RS        is transmitted

A ZP CSI-RS and a PMCH are not configured in the same subframe of aserving cell at the same time.

In the case of a UE in which the transmission mode 10 has beenconfigured, one or more channel state information-interferencemeasurement (CSI-IM) resource configurations may be configured in the UEwith respect to a serving cell.

The following parameters for each CSI-IM resource configuration may beconfigured through high layer signaling.

-   -   The ZP CSI-RS configuration (refer to Table 3 and Table 4)    -   The ZP CSI RS subframe configuration I_CSI-RS (refer to Table 5)

A CSI-IM resource configuration is the same as any one of configured ZPCSI-RS resource configurations.

A CSI-IM resource and a PMCH are not configured within the same subframeof a serving cell at the same time.

Massive MIMO

A MIMO system having a plurality of antennas may be called a massiveMIMO system and has been in the spotlight as means for improvingspectrum efficiency, energy efficiency and processing complexity.

In recent 3GPP, in order to satisfy the requirements of spectrumefficiency for a future mobile communication system, a discussion aboutthe massive MIMO system has started. The massive MIMO is also calledfull-dimension MIMO (FD-MIMO).

In a wireless communication system after LTE Release (Rel)-12, theintroduction of an active antenna system (AAS) is considered.

Unlike the existing passive antenna system in which an amplifier andantenna capable of adjusting the phase and size of a signal have beenseparated, the AAS means a system in which each antenna is configured toinclude an active element, such as an amplifier.

The AAS does not require a separate cable, connector and other hardwarefor connecting an amplifier and an antenna because the active antenna isused, and thus has a high efficiency characteristic in terms of energyand operating costs. In particular, the AAS enables an advanced MIMOtechnology, such as the formation of an accurate beam pattern or 3D beampattern in which a beam direction and a beam width are consideredbecause the AAS supports each electronic beam control method.

Due to the introduction of an advanced antenna system, such as the AAS,a massive MIMO structure having a plurality of input/output antennas anda multi-dimension antenna structure is also considered. For example,unlike in the existing straight type antenna array, if a two-dimensional(2D) antenna array is formed, a 3D beam pattern can be formed by theactive antenna of the AAS.

FIG. 10 illustrates a 2D-AAS having 64 antenna elements in a wirelesscommunication system to which the present invention may be applied.

FIG. 10 illustrates a common 2D antenna array. A case where N_t=N_v·N_hantennas has a square form as in FIG. 10 may be considered. In thiscase, N_h indicates the number of antenna columns in a horizontaldirection, and N_v indicates the number of antenna rows in a verticaldirection.

If the antenna array of such a 2D structure is used, radio waves can becontrolled both in the vertical direction (elevation) and the horizontaldirection (azimuth) so that a transmission beam can be controlled in the3D space. A wavelength control mechanism of such a type may be called 3Dbeamforming.

FIG. 11 illustrates a system in which an eNB or UE has a plurality oftransmission/reception antennas capable of forming a 3D beam based onthe AAS in a wireless communication system to which the presentinvention may be applied.

FIG. 11 is a diagram of the aforementioned example and illustrates a 3DMIMO system using a 2D antenna array (i.e., 2D-AAS).

From the point of view of a transmission antenna, if a 3D beam patternis used, a semi-static or dynamic beam can be formed in the verticaldirection of the beam in addition to the horizontal direction. Forexample, an application, such as the formation of a sector in thevertical direction, may be considered.

Furthermore, from the point of view of a reception antenna, when areception beam is formed using a massive reception antenna, a signalpower rise effect according to an antenna array gain may be expected.Accordingly, in the case of the uplink, an eNB can receive a signal froma UE through a plurality of antennas. In this case, there is anadvantage in that the UE can set its transmission power very low byconsidering the gain of the massive reception antenna in order to reducean interference influence.

FIG. 12 illustrates a 2D antenna system having cross-polarizations in awireless communication system to which the present invention may beapplied.

A 2D planar antenna array model in which polarization is considered maybe diagrammed as shown in FIG. 12.

Unlike the existing MIMO system according to a passive antenna, a systembased on an active antenna can dynamically control the gain of anantenna element by applying weight to an active element (e.g., anamplifier) to which each antenna element has been attached (orincluded). The antenna system may be modeled in an antenna element levelbecause a radiation pattern depends on the number of antenna elementsand an antenna arrangement, such as antenna spacing.

An antenna array model, such as the example of FIG. 12, may berepresented by (M, N, P). This corresponds to a parameter thatcharacterizes an antenna array structure.

M indicates the number of antenna elements having the same polarizationin each column (i.e., the vertical direction) (i.e., the number ofantenna elements having a +45° slant in each column or the number ofantenna elements having a −45° slant in each column).

N indicates the number of columns in the horizontal direction (i.e., thenumber of antenna elements in the horizontal direction).

P indicates the number of dimensions of polarization. P=2 in the case ofcross-polarization as in the case of FIG. 12, or P=1 in the case ofco-polarization.

An antenna port may be mapped to a physical antenna element. The antennaport may be defined by a reference signal related to a correspondingantenna port. For example, in the LTE system, the antenna port 0 may berelated to a cell-specific reference signal (CRS), and the antenna port6 may be related to a positioning reference signal (PRS).

For example, an antenna port and a physical antenna element may bemapped in a one-to-one manner. This may correspond to a case where asingle cross-polarization antenna element is used for downlink MIMO ordownlink transmit diversity. For example, the antenna port 0 is mappedto one physical antenna element, whereas the antenna port 1 may bemapped to the other physical antenna element. In this case, from thepoint of view of a UE, two types of downlink transmission are present.One is related to a reference signal for the antenna port 0, and theother is related to a reference signal for the antenna port 1.

For another example, a single antenna port may be mapped to multiplephysical antenna elements. This may correspond to a case where a singleantenna port is used for beamforming. In beamforming, multiple physicalantenna elements are used, so downlink transmission may be directedtoward a specific UE. In general, this may be achieved using an antennaarray configured using multiple columns of multiple cross-polarizationantenna elements. In this case, from the point of view of a UE, one typeof downlink transmission generated from a single antenna port ispresent. One is related to a CRS for the antenna port 0, and the otheris related to a CRS for the antenna port 1.

That is, an antenna port indicates downlink transmission from the pointof view of a UE not actual downlink transmission from a physical antennaelement by an eNB.

For another example, a plurality of antenna ports is used for downlinktransmission, but each antenna port may be mapped to multiple physicalantenna elements. This may correspond to a case where an antenna arrayis used for downlink MIMO or downlink diversity. For example, each ofthe antenna ports 0 and 1 may be mapped to multiple physical antennaelements. In this case, from the point of view of a UE, two types ofdownlink transmission. One is related to a reference signal for theantenna port 0, and the other is related to a reference signal for theantenna port 1.

In FD-MIMO, the MIMO precoding of a data stream may experience antennaport virtualization, transceiver unit (or a transmission and receptionunit) (TXRU) virtualization, and an antenna element pattern.

In the antenna port virtualization, a stream on an antenna port isprecoded on a TXRU. In the TXRU virtualization, a TXRU signal isprecoded on an antenna element. In the antenna element pattern, a signalradiated by an antenna element may have a directional gain pattern.

In the existing transceiver modeling, a static one-to-one mappingbetween an antenna port and a TXRU is assumed, and a TXRU virtualizationeffect is joined into a static (TXRU) antenna pattern including theeffects of the TXRU virtualization and the antenna element pattern.

The antenna port virtualization may be performed by afrequency-selective method. In LTE, an antenna port, together with areference signal (or pilot), is defined. For example, for precoded datatransmission on an antenna port, a DMRS is transmitted in the samebandwidth as a data signal, and both the DMRS and data are precoded bythe same precoder (or the same TXRU virtualization precoding). For CSImeasurement, a CSI-RS is transmitted through multiple antenna ports. InCSI-RS transmission, a precoder that characterizes mapping between aCSI-RS port and a TXRU may be designed in a unique matrix so that a UEcan estimate a TXRU virtualization precoding matrix for a data precodingvector.

A TXRU virtualization method is discussed in 1D TXRU virtualization and2D TXRU virtualization, which are described below with reference to thefollowing drawing.

FIG. 13 illustrates a transceiver unit model in a wireless communicationsystem to which the present invention may be applied.

In the 1D TXRU virtualization, M_TXRU TXRUs are related to M antennaelements configured in a single column antenna array having the samepolarization.

In the 2D TXRU virtualization, a TXRU model configuration correspondingto the antenna array model configuration (M, N, P) of FIG. 12 may berepresented by (M_TXRU, N, P). In this case, M_TXRU means the number ofTXRUs present in the 2D same column and same polarization, and alwayssatisfies M_TXRU M. That is, the total number of TXRUs is the same asM_TXRU×N×P.

A TXRU virtualization model may be divided into a TXRU virtualizationmodel option-1: sub-array partition model as in FIG. 13(a) and a TXRUvirtualization model option-2: full connection model as in FIG. 13(b)depending on a correlation between an antenna element and a TXRU.

Referring to FIG. 13(a), in the case of the sub-array partition model,an antenna element is partitioned into multiple antenna element groups,and each TXRU is connected to one of the groups.

Referring to FIG. 13(b), in the case of the full-connection model, thesignals of multiple TXRUs are combined and transferred to a singleantenna element (or the arrangement of antenna elements).

In FIG. 13, q is the transmission signal vectors of antenna elementshaving M co-polarizations within one column. W is a wideband TXRUvirtualization vector, and W is a wideband TXRU virtualization matrix. Xis the signal vectors of M_TXRU TXRUs.

In this case, mapping between an antenna port and TXRUs may beone-to-one or one-to-many.

In FIG. 13, mapping between a TXRU and an antenna element(TXRU-to-element mapping) shows one example, but the present inventionis not limited thereto. From the point of view of hardware, the presentinvention may be identically applied to mapping between an TXRU and anantenna element which may be implemented in various forms.

Codebook Design Method for 3D MIMO System Operating Based on 2D AAS

As illustrated in FIGS. 10 to 12, the present invention proposes amethod of configuring (designing) a codebook on the basis of DFT(discrete Fourier transform) for 2D AAS.

Inn LTE-A, a PMI (precoding matrix indicator) of an 8 Tx (transmitter)codebook is designed as a long term and/or wideband precoder W_1 and ashort term and/or sub-band precoder W_2 in order to improve feedbackchannel accuracy.

An equation for configuring a final PMI from two pieces of channelinformation is represented by the product of W_1 and W_2 as expressed byEquation 15.

W=norm(W ₁ W ₂)  [Equation 15]

In Equation 15, W is a precoder generated from W_1 and W_2 and is fedback to a base station from a UE. norm(A) represents a matrix in which anorm per column in a matrix A is normalized to 1.

In the 8Tx codebook defined in LTE, W_1 and W_2 have structures asrepresented by Equation 16.

$\begin{matrix}{{{W_{1}\left( i_{1} \right)} = \begin{bmatrix}X_{i_{1}} & 0 \\0 & X_{i_{1}}\end{bmatrix}},{{{where}\mspace{14mu} X_{i_{1}}\mspace{14mu} {is}\mspace{14mu} {Nt}\text{/}2\mspace{14mu} {by}\mspace{14mu} M\mspace{14mu} {{matrix}.{W_{2}\left( i_{2} \right)}}} = {\overset{r\mspace{14mu} {columns}}{\overset{}{\begin{bmatrix}e_{M}^{k} & e_{M}^{l} & \; & e_{M}^{m} \\\; & \; & \ldots & \; \\{\alpha_{i_{2}}e_{M}^{k}} & {\beta_{i_{2}}e_{M}^{j}} & \; & {\gamma_{i_{2}}e_{M}^{m}}\end{bmatrix}}}\mspace{14mu} \left( {{{if}\mspace{14mu} {rank}} = r} \right)}},{{{where}\mspace{14mu} 1} \leq k},l,{m \leq {M\mspace{14mu} {and}\mspace{14mu} k}},l,{m\mspace{14mu} {are}\mspace{14mu} {{integer}.}}} & \left\lbrack {{Equation}\mspace{14mu} 16} \right\rbrack\end{matrix}$

Here, i_1 and i_2 respectively indicate indexes of W_1 and W_2 and e_(M)^(k) represents a selection vector having a length of M, in which thevalue of a k-th element is 1 and other values are 0.

The aforementioned codeword structure is designed in consideration ofchannel correlation characteristics generated when cross polarizedantennas are used and an antenna spacing is narrow (e.g., a distancebetween adjacent antennas is less than half a signal wavelength). Crosspolarized antennas can be divided into a horizontal antenna group and avertical antenna group. Each antenna group has characteristics of auniform linear array (ULA) antenna and the two antenna groups may beco-located. Accordingly, correlation between antennas of each group hasthe same linear phase increment characteristic and correlation betweenantenna groups has phase rotation characteristic.

Since a codebook corresponds to values obtained by quantizing channels,it is necessary to design the codebook by reflecting characteristics ofa channel corresponding to a source therein.

When a rank-1 codeword generated in the above structure is exemplifiedfor convenience of description, it can be confirmed that such channelcharacteristics have been reflected in a codeword that satisfiesEquation 16.

$\begin{matrix}{{{W_{1}\left( i_{1} \right)}*{W_{2}\left( i_{2} \right)}} = \begin{bmatrix}{X_{i_{1}}(k)} \\{\alpha_{i_{2}}{X_{i_{1}}(k)}}\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 17} \right\rbrack\end{matrix}$

In Equation 17, the codeword is represented by N_t (the number of Txantennas)×1 and structurized into an upper vector X_(i) ₁ (k) and alower vector α_(i) ₂ X_(i) ₁ (k) which respectively representcorrelation characteristics of the horizontal antenna group and thevertical antenna group. It is advantageous to represent X_(i) ₁ (k) as avector having linear phase increment by reflecting inter-antennacorrelation characteristic of each antenna group therein, and a DFTmatrix can be used therefor as a typical example.

This codebook structure is applicable to systems using 2D AAS and isrepresented by Equation 18.

w=W ₁ W ₂=(w _(1H) ⊗W _(1V))(W _(2H) ⊗W _(2V))  [Equation 18]

Here, W_1 represents long-term properties of a channel and is fed backwith respect to widebands, and W_2 represents short-term properties of achannel, is fed back with respect to subbands and performs selection andco-phasing (in the case of cross polarized antennas). The subscripts Hand V represent horizontal and vertical directions and ⊗ denotes aKronecker product.

W_1V is selected as a subset of a matrix D composed of columns in thematrix D of a DFT codebook, as represented by Equation 19. The DFTcodebook can be generated as represented by Equation 19.

$\begin{matrix}{{D_{({mn})}^{N_{v} \times N_{v}Q_{v}} = {\frac{1}{\sqrt{N_{v}}}e^{j\frac{2{\pi {({m - 1})}}{({n - 1})}}{N_{v}Q_{v}}}}},{{{for}\mspace{14mu} m} = 1},2,\cdots,N_{v},{n = 1},2,\cdots,{N_{v}Q_{v}}} & \left\lbrack {{Equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$

In Equation 19, Q_(v) denotes an oversampling factor and N_(v)represents the number of vertical antenna ports.

Here, an antenna element may correspond to an antenna port according toantenna virtualization. Hereinafter, an antenna element will be calledan antenna port in the specification for convenience of description.

Similarly, W_1H is selected as a subset of the matrix D composed ofcolumns in the matrix D as represented by Equation 20. A DFT codebookcan be generated as represented by Equation 20.

$\begin{matrix}{{D_{({mn})}^{N_{h} \times N_{h}Q_{h}} = {\frac{1}{\sqrt{N_{h}}}e^{j\frac{2{\pi {({m - 1})}}{({n - 1})}}{N_{h}Q_{h}}}}},{{{for}\mspace{14mu} m} = 1},2,\cdots,N_{h},{n = 1},2,\cdots,{N_{h}Q_{h}}} & \left\lbrack {{Equation}\mspace{14mu} 20} \right\rbrack\end{matrix}$

In Equation 20, Q_(h) denotes an oversampling factor and N_(h) is thenumber of horizontal antenna ports.

As described above, the precoding matrix W in a codebook can berepresented as W=W₁W₂. Here, W1 can be derived as

$W_{1} = {\begin{pmatrix}{X_{1} \otimes X_{2}} & 0 \\0 & {X_{1} \otimes X_{2}}\end{pmatrix}.}$

Here, X₁ is an N_1×L_1 matrix and can be composed of L_1 column vectors.The column vectors have a length of N_1 and can correspond to a DFTvector oversampled O_1 times, that is,

$v_{l} = {\left\lbrack {1\mspace{14mu} e^{\frac{j\; 2\pi \; l}{N_{1}O_{1}}}\mspace{14mu} \ldots \mspace{14mu} e^{\frac{j\; 2{\pi {({N_{1} - 1})}}l}{N_{1}O_{1}}}} \right\rbrack^{t}.}$

In addition, X₂ is an N_2×L_2 matrix and can be composed of L_2 columnvectors. Here, the column vectors have a length of N_2 and cancorrespond to a DFT vector oversampled O_2 times, that is, v_(l)=

$\left\lbrack {1\mspace{14mu} e^{\frac{j\; 2\pi \; l}{N_{2}O_{2}}}\mspace{14mu} \ldots \mspace{14mu} e^{\frac{j\; 2{\pi {({N_{2} - 1})}}l}{N_{2}O_{2}}}} \right\rbrack^{t}.$

Here, N_1 represents the number of antenna ports for the samepolarization in the first dimension (e.g., horizontal domain) and N_2represents the number of antenna ports for the same polarization in thesecond dimension (e.g., vertical domain).

FIG. 14 illustrates a 2D AAS in a wireless communication system to whichthe present invention is applicable.

FIG. 14(a) illustrates an 8 transceiver unit (TXRU: transceiver unit) 2DAAS, FIG. 14(b) illustrates a 12 TXRU 2D AAS and FIG. 14(c) illustratesa 16 TXRU 2D AAS.

In FIG. 14, M is the number of antenna ports of a single column (i.e.,the first dimension) which have the same polarization and N is thenumber of antenna ports of a single row (i.e., the second dimension)which have the same polarization. P indicates the number of dimensionsof polarization. Q indicates the total number of TXRUs (antenna ports).

The codebook proposed in the present invention is applicable to the 2DAAS illustrated in FIG. 14. The present invention is not limited to the2D AAS illustrated in FIG. 14 and may be extended and applied to antennaconfigurations other than the antenna configuration of FIG. 14.

First, a case of (M, N, P, Q)=(2, 2, 2, 8) will be described. In thiscase, two +45° slant antennas (antennas “/” in FIG. 14) are located inthe horizontal direction and the vertical direction, and N_(h)=2,N_(v)=2.

The numbers of columns (i.e., the numbers of precoding matrices) thatform codebooks constituting W_1H and W_1V according to an oversamplingfactor Q_(h) in the horizontal direction and an oversampling factorQ_(v) in the vertical direction are N_(h)Q_(h) and N_(h)Q_(v),respectively. The codebook C_1 constituting W_1 is composed ofKroenecker product of codebooks corresponding to horizontal and verticalantenna ports, and thus the number of columns constituting the codebookC_1 is N_(h)Q_(h)N_(v)Q_(v), and in the case of 8 TXRUs, 4Q_(h)Q_(v).

In this manner, various types of codebooks can be configured accordingto oversampling factors and the number of bits of a PMI fed back from areception terminal to a base station.

Hereinafter, the number of feedback bits corresponding to W_1 is definedas L_1 and the number of feedback bits corresponding to W_2 is definedas L_2.

In addition, the aforementioned parameters N_(h), Q_(h), N_(v) and Q_(v)may have different values depending on the number of antenna ports, asillustrated in FIG. 14, and signaled by a base station to a terminalthrough RRC signaling or values predefined between the base station andthe terminal may be used as the parameters.

The present invention proposes a method of configuring/setting W_1 andW_2 in codebook design for a 2D AAS in which at least matrix W_1 has adual structure.

In the following description of the present invention, the firstdimension/domain is referred to as a horizontal dimension/domain and thesecond dimension/domain is referred to as a vertical dimension/domain ina 2D antenna array for convenience of description. However, the presentinvention is not limited thereto.

Furthermore, in description of the present invention, the same variablesused in equations can be indicated by the same signs and construed asthe same meaning unless specially described.

In addition, in description of the present invention, a beam can beconstrued as a precoding matrix for generating the beam and a beam groupcan be construed as a set of precoding matrices (or a set of precodingvectors). Further, selection of a beam (or a beam pair) can be construedas selection of a precoding matrix (or vector) capable of generating thebeam.

1. 8 TXRU

A method of configuring a codebook for an 8 TXRU 2D AAS as shown in FIG.14(a) will be described. It is assumed that Q_(h)=4, Q_(v)=2, L₁=4,L₂=4.

In this case, the number of columns constituting a codebook C1 is 32(=N_(h)Q_(h)N_(v)Q_(v)=2*4*2*2). Each column is composed of 4 Tx DFTvectors.

A reception UE can report (i.e., feed back), to a base station (BS), aW_1 index suitable therefor in terms of long-term/wideband among thecolumns using a reference signal (e.g., CSI-RS) transmitted from the BS.

Here, a method of configuring W_1 corresponding to each index may becorrelated with L_2 which is the number of feedback bits of W_2 matrixin charge of selection and co-phasing. The number of bits correspondingto selection is defined as L_2S and the number of bits corresponding toco-phasing is defined as L_2C for convenience. Here, the relationship ofL_2=L_2S+L_2C is established.

For example, in the case of L_2S=2, W_1 corresponding to each index canbe composed of 2²=4 columns. In this case, a method of configuring W_1and W_2 is as follows.

First, an inner precoder W₁ can be selected from the first codebook C₁.

In an embodiment of the present invention, W_1 can be configured asrepresented by Equation 21.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{4\mspace{14mu} {columns}}{\underset{}{w_{{{({{2i_{1}} + 0})}{mod}\; 8} + {8{\lfloor\frac{i_{1}}{4}\rfloor}}}\mspace{14mu} w_{{{({{2i_{1}} + 1})}{mod}\; 8} + {8{\lfloor\frac{i_{1}}{4}\rfloor}}}\mspace{14mu} w_{{{({{2i_{1}} + 2})}{mod}\; 8} + {8{\lfloor\frac{i_{1}}{4}\rfloor}}}\mspace{14mu} w_{{{({{2i_{1}} + 3})}{mod}\; 8} + {8{\lfloor\frac{i_{1}}{4}\rfloor}}}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 8}},{v = \left\lfloor \frac{m}{8} \right\rfloor},{m \in \left\{ {{\left( {{2i_{1}} + i_{2}} \right)\mspace{14mu} {mod}\mspace{14mu} 8} + {8\left\lfloor \frac{i_{1}}{4} \right\rfloor}} \right\}},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 21} \right\rbrack\end{matrix}$

Here, i_1 indicates an index of W_1 (i.e., a set of precoding matrices)(i.e., a first PMI for specifying W_1) and i_2 is an index correspondingto selection of W_2 (i.e., a second PMI for specifying a precodingmatrix selected from the set of precoding matrices).

As described above, the number of columns constituting the codebook C1is N_(h)Q_(h)N_(v)Q_(v) (32 in the case of Equation 21), and each columncorresponds to a precoding matrix (or precoding vector) W_m and can beidentified by the index m.

Further, precoding matrices constituting the codebook C1 can berepresented in a 2-dimensional form (refer to FIG. 15). In this case,each precoding matrix W_m can be specified by the index h in the firstdimension (i.e., horizontal dimension) and the index v in the seconddimension (i.e., vertical dimension). That is, the index m can beone-to-one mapped to an index pair such as (h,v).

In addition, a first matrix (or a first vector) (e.g., a matrix (or avector) having horizontal elements) v_h for first dimension antennaports can be specified by the index h of the first dimension and asecond matrix (or a second vector) (e.g., a matrix (or a vector) havingvertical elements) v_v for second dimension antenna ports can bespecified by the index v of the second dimension. In addition, w_m has aDFT matrix form and can be generated as the Kronecker product of v_h andv_v.

A precoding matrix set composed of one or more precoding matrices (e.g.,4 precoding matrices) may be determined by i_1 in the entire codebook,and one precoding matrix may be determined by i_2 in the determinedprecoding matrix set. In other words, the precoding matrix index m orprecoding index pair values (h, v) of one or more precoding matricesbelonging to the precoding matrix set may be determined by i_1. Inaddition, one precoding matrix index m or precoding index pair value (h,v) may be determined by i_2 in the determined percoding matrix set.

The above equation 21 can be represented as the diagram of FIG. 15.

FIG. 15 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

In FIG. 15, numerals 0 to 31 indicate indexes of columns (i.e.,precoding matrices w_m) constituting the entire codebook C_1. That is,the numerals indicate indexes m of all precoding matrices. m can have avalue in the range of 0 to N_h*Q_h*N_v*Q_v.

Furthermore, in FIG. 15, the columns (i.e., precoding matrices w_m)constituting the entire codebook C_1 are arranged in a 2-dimensionalform. h and v indicate an index of a horizontal component of each column(i.e., precoding matrix w_m) constituting the entire codebook C_1 (i.e.,an index of a horizontal component of a DFT vector constituting w_m) andan index of a vertical component of each column (i.e., an index of avertical component of the DFT vector constituting w_m). That is, h mayhave a value in the range of 0 to N_h*Q_h (0 to 7 in FIG. 15) and v mayhave a value in the range of 0 to N_v*Q_v (0 to 3 in FIG. 15).

Furthermore, each box shown in FIG. 15 represents W_1(i_1) (i.e., W_1(0), W_1 (1), W_1 (2) and W_1 (3)). That is, the box of W_1(i_1) can bedetermined by i_1. Referring to FIG. 15, W_1(0) can be composed of aprecoding matrix with m=0, 1, 2 and 3. When this is represented as pairsof indexes in the horizontal dimension and indexes in the verticaldimension, a precoding matrix with (h,v)=(0,0), (1,0), (2,0) and (3,0)can be configured. W_1 (1) can be composed of a precoding matrix withm=2, 3, 4 and 5 (i.e., precoding matrix with (h,v)=(2,0), (3,0), (4,0)and (5,0)). W_1 (2) can be composed of a precoding matrix with m=4, 5, 6and 7 (i.e., precoding matrix with (h,v)=(4,0), (5,0), (6,0) and (7,0)).W_1 (3) can be composed of a precoding matrix with m=6, 7, 0 and 1(i.e., precoding matrix with (h,v)=(6,7), (7,0), (0,0) and (1,0)). W_1(4) and W_1 (15) can be configured in the same manner.

In this manner, W_1 is composed of subsets of 4 horizontal componentsfor a fixed (identical) vertical component and 2 horizontal componentsmay overlap in consecutive (adjacent) W_1s. That is, 2 precodingmatrices overlap between W_1s which are consecutive (adjacent) in thehorizontal dimension direction. In other words, the spacing betweenprecoding matrix sets which are consecutive (adjacent) in the horizontaldimension direction can be 2. For example, precoding matrices w_mconstituting W_1s having indexes of 0 to 3 can be composed of the samevertical component matrix

$v_{v} = {\begin{bmatrix}1 \\e^{j\frac{2{\pi 0}}{4}}\end{bmatrix}.}$

When the method of configuring W_1 as illustrated in FIG. 15 isgeneralized, pairs of indexes in the first dimension and indexes in thesecond dimension of a precoding matrix constituting W_1 may correspondto (x,y), (x+1,y), (x+2,y) and (x+3,y). Here, x and y are integers thatare not negative numbers.

The aforementioned index pairs may be represented as (h,v), (h+1,v),(h+2,v) and (h+3,v) in the horizontal dimension and the verticaldimension. In the same manner, indexes x and y may be replaced by h andv the horizontal dimension and the vertical dimension in other codebookconfiguration methods described in the specification.

x may have a value depending on the spacing between precoding matrixsets which are consecutive (adjacent) in the horizontal dimensiondirection. For example, when the spacing is 2 in the first dimension(e.g., horizontal dimension) direction as shown in FIG. 15, x may have avalue corresponding to a multiple of 2. When the spacing is 1 in thefirst dimension (e.g., horizontal dimension) direction, x may have avalue corresponding to a multiple of 1. In the same manner, y may have avalue depending on the spacing between precoding matrix sets which areconsecutive (adjacent) in the vertical dimension direction.

In the following description of the present invention, description ofthe same parts as those in Equation 21 and FIG. 15 is omitted anddifferent parts are described.

As another embodiment, W_1 may be configured as represented by Equation22.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{4\mspace{14mu} {columns}}{\underset{}{w_{{{(i_{1})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}}\mspace{14mu} w_{{{({i_{1} + 1})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}}\mspace{14mu} w_{{{(i_{1})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + 8}\mspace{14mu} w_{{{({i_{1} + 1})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + 8}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 8}},{v = \left\lfloor \frac{m}{8} \right\rfloor},{m \in \left\{ {{\left( {i_{1} + {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2}} \right)\mspace{14mu} {mod}\mspace{14mu} 8} + {16\left\lfloor \frac{i_{1}}{8} \right\rfloor} + {8\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right\}},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 22} \right\rbrack\end{matrix}$

Equation 22 is represented as the diagram of FIG. 16.

FIG. 16 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 16, each W_1 has 2 vertical components and 2horizontal components and one horizontal component overlap betweenconsecutive W_1s. That is, 2 precoding matrices overlap between W_1sconsecutive (neighboring) in the horizontal dimension direction. Thatis, the spacing between precoding matrix sets consecutive (neighboring)in the horizontal dimension direction can correspond to 1.

For example, when W_1 has an index in the range of 0 to 7, w_m includedin W_1 can be composed of vertical component matrices

${v_{v} = \begin{bmatrix}1 \\e^{j\frac{2{\pi 0}}{4}}\end{bmatrix}},{v_{v} = {\begin{bmatrix}1 \\e^{j\frac{2{\pi 1}}{4}}\end{bmatrix}.}}$

When W_1 has an index in the range of 8 to 15, w_m included in W_1 canbe composed of vertical component matrices

${v_{v} = \begin{bmatrix}1 \\e^{j\frac{2{\pi 2}}{4}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2{\pi 3}}{4}}\end{bmatrix}}$

When the method of configuring W_1 shown in FIG. 16 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 can correspond to(x,y), (x+1,y), (x,y+1) and (x+1,y+1). Here, x and y are integers thatare not negative numbers.

x may have a value depending on the spacing between precoding matrixsets consecutive (neighboring) in the horizontal dimension direction.For example, when the spacing is 2 in the first dimension (e.g.,horizontal dimension) direction, x may have a value corresponding to amultiple of 2. On the other hand, when the spacing is 1 in thehorizontal dimension direction as shown in FIG. 16, x may have a valuecorresponding to a multiple of 1. In the same manner, y may have a valuedepending on the spacing between precoding matrix sets consecutive(neighboring) in the vertical dimension direction.

As another embodiment, W_1 may be configured as represented by Equation23.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{4\mspace{14mu} {columns}}{\underset{}{w_{{{(i_{1})}{mod}\; 8} + {8{\lfloor\frac{i_{1}}{8}\rfloor}}}\mspace{14mu} w_{{{({i_{1} + 1})}{mod}\; 8} + {8{\lfloor\frac{i_{1}}{8}\rfloor}}}\mspace{14mu} w_{{{(i_{1})}{mod}\; 8} + {8{\lfloor\frac{i_{1}}{8}\rfloor}} + {8\mu}}\mspace{14mu} w_{{{({i_{1} + 1})}{mod}\; 8} + {8{\lfloor\frac{i_{1}}{8}\rfloor}} + {8\mu}}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 8}},{v = \left\lfloor \frac{m}{8} \right\rfloor},{m \in \left\{ {{\left( {i_{1} + {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2}} \right)\mspace{14mu} {mod}\mspace{14mu} 8} + {8\left\lfloor \frac{i_{1}}{8} \right\rfloor} + {8\mu \left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right\}},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 23} \right\rbrack\end{matrix}$

Equation 23 is represented as the diagram of FIG. 17.

FIG. 17 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 17, the length of the vertical domain can be set to μduring beam grouping. FIG. 17 illustrates a case in which μ=2.

When the method of configuring W_1 shown in FIG. 17 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 can correspond to(x,y), (x+1,y), (x,y+μ) and (x+1,y+μ). Here, x and y are integers thatare not negative numbers.

In addition, 2 precoding matrices overlap between W_1s consecutive(neighboring) in the horizontal dimension direction. That is, thespacing between precoding matrix sets consecutive (neighboring) in thehorizontal dimension direction can correspond to 1.

As another embodiment, W_1 may be configured as represented by Equation24.

$\begin{matrix}{\left. {{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{4\mspace{14mu} {columns}}{\underset{}{w_{{({2i_{1}})}{mod}\; 32}\mspace{14mu} w_{{({{2i_{1}} + 1})}{mod}\; 32}\mspace{14mu} w_{{({{2i_{1}} + 8})}{mod}\; 32}\mspace{14mu} w_{{({{2i_{1}} + 9})}{mod}\; 32}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 8}},{v = \left\lfloor \frac{m}{8} \right\rfloor},{m \in {\left\{ {{\left( {{2i_{1}} + i_{2}} \right)\mspace{14mu} {mod}\mspace{14mu} 2} + {8\left\lfloor \frac{i_{1}}{2} \right\rfloor}} \right){mod}\mspace{14mu} 32}}}} \right\},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3.} & \left\lbrack {{Equation}\mspace{14mu} 24} \right\rbrack\end{matrix}$

Here, i_1 indicates an index of W_1 and i_2 is an index corresponding toselection of W_2.

Equation 24 is represented as the diagram of FIG. 18.

FIG. 18 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 18, each W_1 has 2 vertical components and 2horizontal components, and one vertical component overlaps betweenconsecutive W_1s. That is, 2 precoding matrices overlap between W_1sconsecutive (neighboring) in the vertical dimension direction. That is,the spacing between precoding matrix sets consecutive (neighboring) inthe vertical dimension direction can correspond to 1.

For example, when the index of W_1 is {0,4,8,12}, w_m included in W_1can be composed of horizontal component matrices

${v_{h} = \begin{bmatrix}1 \\e^{j\frac{2{\pi 0}}{8}}\end{bmatrix}},{v_{h} = {\begin{bmatrix}1 \\e^{j\frac{2{\pi 1}}{8}}\end{bmatrix}.}}$

When the index of W_1 is {1,5,9,13}, w_m included in W_1 can be composedof horizontal component matrices

${v_{h} = \begin{bmatrix}1 \\e^{j\frac{2{\pi 2}}{8}}\end{bmatrix}},{v_{h} = {\begin{bmatrix}1 \\e^{j\frac{2{\pi 3}}{8}}\end{bmatrix}.}}$

When the method of configuring W_1 shown in FIG. 18 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x+1,y) and (x+1,y+1). Here, x and y are integers that are notnegative numbers.

In addition, 2 precoding matrices overlap between W_1s consecutive(neighboring) in the vertical dimension direction. That is, the spacingbetween precoding matrix sets consecutive (neighboring) in the verticaldimension direction can correspond to 1.

As another embodiment, W_1 may be configured as represented by Equation25.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{4\mspace{14mu} {columns}}{\underset{}{w_{{{(i_{1})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}}\mspace{14mu} w_{{{({i_{1} + 2})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}}\mspace{14mu} w_{{{({i_{1} + 2})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + 8}\mspace{14mu} w_{{{({i_{1} + 3})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + 8}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 8}},{v = \left\lfloor \frac{m}{8} \right\rfloor},{m \in \left\{ {{\left( {i_{1} + {2 \cdot \left( {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2} \right)} + \left\lfloor \frac{i_{1}}{2} \right\rfloor} \right){mod}\mspace{14mu} 8} + {16\left\lfloor \frac{i_{1}}{8} \right\rfloor} + {8\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right\}},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 25} \right\rbrack\end{matrix}$

Equation 25 is represented as the diagrams of FIGS. 19 and 20.

FIG. 19 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 19, W_1 may be configured in a zigzag pattern (orcheck pattern). That is, W_1 (0) can be composed of {w_0, w_2, w_9,w_11}.

When the method of configuring W_1 shown in FIG. 19 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+2,y), (x+1,y+1) and (x+3,y+1). Here, x and y are integers that arenot negative numbers.

In addition, 2 precoding matrices overlap between W_1s consecutive(neighboring) in the horizontal dimension direction. That is, thespacing between precoding matrix sets consecutive (neighboring) in thehorizontal dimension direction can correspond to 2.

In the example of FIG. 19, the pattern of W_1 corresponds to a case inwhich beam groups of W_1 are {w_0, w_2, w_9, w_11}.

Further, W_1 may be configured as a complementary set of the zigzagpattern (or check pattern).

FIG. 20 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

FIG. 20 illustrates a case in which the zigzag pattern (check pattern)as shown in FIG. 19 corresponds to a complementary set of {w_1, w_3,w_8, w_10} in a 2×4 rectangular beam group composed of {w_0, w_1, w_2,w_3, w_8, w_9, w_10, w_11}.

When the method of configuring W_1 shown in FIG. 20 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x+1,y),(x,y+1), (x+2,y+1) and (x+3,y). Here, x and y are integers that are notnegative numbers.

FIG. 20 illustrates a case in which the spacing between W_1 beam groups(i.e., precoding matrix sets) is 2, and it is obvious that theabove-described embodiments with respect to the zigzag patterns (orcheck patterns) are easily applicable to the zigzag pattern (or checkpattern) which will be described below.

Cases in which the spacing between indexes of horizontally adjacentprecoding matrix sets is 1 or 2 in the aforementioned zigzag patterns(or check patterns) have been described above. This can be generalizedand represented by the following equation 26.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{4\mspace{14mu} {columns}}{\underset{}{w_{{({{{(i_{1})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}})}{mod}\; 32}\mspace{14mu} w_{{({{{({i_{1} + 2})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}})}{mod}\; 32}\mspace{14mu} w_{{({{{({i_{1} + 2})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + {8c}})}{mod}\; 32}\mspace{14mu} w_{{({{{({i_{1} + 3})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + {8c}})}{mod}\; 32}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 8}},{v = \left\lfloor \frac{m}{8} \right\rfloor},{m \in \left\{ {\left( {{\left( {i_{1} + {a \cdot \left( {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2} \right)} + {b\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\mspace{14mu} 8} + {16\left\lfloor \frac{i_{1}}{8} \right\rfloor} + {8c\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\; 32} \right\}},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 26} \right\rbrack\end{matrix}$

Equation 26 is represented as the diagram of FIG. 21.

FIG. 21 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 21, column indexes are spaced by values a and b in thehorizontal direction and spaced by a value c in the vertical directionin w_m constituting W_1.

When the method of configuring W_1 shown in FIG. 21 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+a,y), (x+b,y+c) and (x+a+b,y+c). Here, x and y are integers that arenot negative numbers.

In the above-described zigzag pattern configuration method, B_(k) W_1 sare present in the horizontal direction and B_(v)/2 W_1 groups arepresent in the vertical direction. Similarly, a pattern in which B_(k)/2W_1s are arranged in the horizontal direction and B_(v) 4 W_1 groups arearranged can be generated and is represented by Equation 27.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{4\mspace{14mu} {columns}}{\underset{}{w_{{({{{(i_{1})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}})}{mod}\; 32}\mspace{14mu} w_{{({{{({i_{1} + 2})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}})}{mod}\; 32}\mspace{14mu} w_{{({{{({i_{1} + 2})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + {8c}})}{mod}\; 32}\mspace{14mu} w_{{({{{({i_{1} + 3})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + {8c}})}{mod}\; 32}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 8}},{v = \left\lfloor \frac{m}{8} \right\rfloor},{m \in \left\{ {\left( {{\left( {{2i_{1}} + {a \cdot \left( {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2} \right)} + {b\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\mspace{14mu} 8} + {8\left\lfloor \frac{i_{1}}{4} \right\rfloor} + {8c\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\; 32} \right\}},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 27} \right\rbrack\end{matrix}$

Equation 26 normalizes the zigzag pattern (or check pattern). In FIG.26, the aforementioned square pattern (refer to FIG. 18) can be derivedby adjusting the 3 parameters a, b and c. That is, when a is set to −1,b is set to 0 and c is set to 0 in Equation 26, a square pattern (referto FIG. 18) can be derived. Alternatively, a block-shaped pattern asshown in FIG. 22 may be derived.

FIG. 22 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 22, when a is set to 0, b is set to 2 and c is set to0 in Equation 26, a pattern as shown in FIG. 22(a) can be configured. Inthe case of patterns of FIG. 22, all regions of a grid of beam (GoB) canbe covered without overlap between beam groups when a beam group spacingis set to 2.

When the method of configuring W_1 shown in FIG. 22(a) is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x+2,y+1) and (x+3,y+1). Here, x and y are integers that arenot negative numbers.

FIG. 22(b) illustrates complementary sets of FIG. 22(a) in a 2×4 beamgroup. Pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1, as shown in FIG.22(b), correspond to (x,y+1), (x+1,y+1), (x+2,y) and (x+3,y). Here, xand y are integers that are not negative numbers.

In addition, as patterns having the aforementioned characteristics, “V”patterns as shown in FIG. 23 can also be considered.

FIG. 23 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

When the 3 parameters a, b and c are adjusted in Equation 26, a “V”pattern can be derived as shown in FIG. 23(a). When the method ofconfiguring W_1 as shown in FIG. 23(a) is generalized, pairs of indexesin the first dimension and indexes in the second dimension of precodingmatrices constituting W_1 correspond to (x,y), (x+1,y+1), (x+2,y+1) and(x+3,y). Here, x and y are integers that are not negative numbers.

FIG. 23(b) illustrates complementary sets of FIG. 23(a) in a 2×4 beamgroup.

When the method of configuring W_1 as shown in FIG. 23(b) isgeneralized, pairs of indexes in the first dimension and indexes in thesecond dimension of precoding matrices constituting W_1 correspond to(x,y+1), (x+1,y), (x+2,y) and (x+3,y+1). Here, x and y are integers thatare not negative numbers.

FIG. 23(c) illustrates an embodiment of a V pattern. In this case, 8beams are present in the horizontal direction and the spacing betweenbeam groups is 2 in the horizontal direction.

In the case of the above-described patterns of FIGS. 22 and 23, theentire GoB can be covered, but when codebook subsampling of selectingeven-numbered or odd-numbered W_1 is considered, GoB is covered lessuniformly than the zigzag patterns (or check patterns) illustrated inFIG. 19 and FIG. 20 when subsampling is permitted and thus performancedeterioration may occur.

Embodiments in which W_1 is composed of 4 columns have been described.Methods of configuring W_2 when these embodiments will be described.

In the case of transmission rank of 1, an outer precoder W₂ can beselected from the second codebook C₂ ⁽¹⁾.

In the case of rank 1, W_1 is configured as described above and one ofprecoding matrices (or vectors) included in W_1 can be selected.

In an embodiment of the present invention, W_2 may be configured asrepresented by Equation 28.

$\begin{matrix}{{C_{2}^{(1)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{\phi \; Y}\end{bmatrix}} \right\}},{Y \in \left\{ {e_{1},e_{2},e_{3},e_{4}} \right\}},{\phi \in {\left\{ {1,{- 1},{j - j}} \right\}.}}} & \left\lbrack {{Equation}\mspace{14mu} 28} \right\rbrack\end{matrix}$

Here, e_(k) is a selection vector in which only a k-th element has avalue of 1 and other elements have a value of 0. The value (i.e., one of1 to 4) of k (i.e., selection index) is determined by i_2.

That is, the k-th precoding matrix is selected from precoding matricesbelonging to the precoding matrix set W_1, and k may refer to the indexfor identifying a precoding matrix belonging to the precoding matrixset.

Here, k may be sequentially indexed from the left to the right of w_mbelonging to W_1 in the equation for configuring W_1 such as Equation21.

Alternatively, with respect to precoding matrices w_m belonging to theprecoding matrix set W_1, k may be sequentially indexed in increasingorder of index (i.e., x or h) of the first dimension and then inincreasing order of index (i.e., y or v) of the second dimension. Forexample, {w_0, w_2, w_9, w_11} can be sequentially indexed with k={1, 2,3, 4} in the example of FIG. 19. Conversely, k may be sequentiallyindexed in increasing order of index (i.e., y or v) of the seconddimension and then in increasing order of index (i.e., x or h) of thefirst dimension. For example, {w_0, w_9, w_2, w_11} can be sequentiallyindexed with k={1, 2, 3, 4} in the example of FIG. 19.

Alternatively, with respect to precoding matrices w_m belonging to theprecoding matrix set W_1, k may be indexed in increasing order of index(i.e., x or h) of the first dimension. For example, {w_0, w_9, w_2,w_11} can be sequentially indexed with k={1, 2, 3, 4} in the example ofFIG. 19.

φ performs co-phasing between polarization antenna port groups. In otherwords, φ indicates a factor for controlling phase between first andsecond antenna ports in a cross-polarization antenna and can bedetermined as one of

${\exp \left( {j\frac{\pi}{2}} \right)},{{\exp \left( {j\frac{2\pi}{2}} \right)}\mspace{14mu} {and}\mspace{14mu} {{\exp \left( {j\frac{3\pi}{2}} \right)}.}}$

As represented in Equation 28, L_2 is 4 bits because L_2S=2 and L_2C=2

As illustrated in FIGS. 15 to 20, two beams overlap between adjacentW1s. That is, as in the example of FIG. 15, W_1(0) is composed of a beamgroup of {0,1,2,3}, W_1 (1) is composed of a beam group of {2,3,4,5},and {2,3} overlaps. In this case, as a method for increasing beamresolution of all codebooks, the selection vector e_(i) can bemultiplied by a rotation coefficient (e.g.,

$\alpha_{i} = {{\exp \left( \frac{j\; 2{\pi \left( {i - 1} \right)}}{N_{h}Q_{h}} \right)}.}$

Here, the rotation coefficient can correspond to

${\alpha_{i} = {\exp \left( {j\frac{2{{\pi 2}\left( {i - 1} \right)}}{N_{v}Q_{v}}} \right)}},{\alpha_{i} = {\exp \left( {j\frac{2{{\pi 2}\left( {i - 1} \right)}}{N_{h}Q_{h}N_{v}Q_{v}}} \right)}}$

or any rotation coefficient adapted to system performance.

More specifically, the rotation coefficient can be set to

${\alpha_{i} = {\exp \left( {j\frac{2{{\pi 2}\left( {i - 1} \right)}}{32}} \right)}},{\alpha_{i} = {\exp \left( {j\frac{2{{\pi 2}\left( {i - 1} \right)}}{16}} \right)}},{\alpha_{i} = {\exp \left( {j\frac{2{{\pi 2}\left( {i - 1} \right)}}{8}} \right)}},{\alpha_{i} = {\exp \left( {j\frac{2{{\pi 2}\left( {i - 1} \right)}}{4}} \right)}}$

or an arbitrary value.

In this case, Equation 28 can be represented as Equation 29.

$\begin{matrix}{{C_{2}^{(1)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{\alpha_{i}\varphi \; Y}\end{bmatrix}} \right\}},{Y \in \left\{ {e_{1},e_{2},e_{3},e_{4}} \right\}},{\varphi \in {\left\{ {1,{- 1},j,{- j}} \right\}.}}} & \left\lbrack {{Equation}\mspace{14mu} 29} \right\rbrack\end{matrix}$

Here, i is the index of the selection vector e_(i).

In the case of transmission rank 2, the outer precoder W₂ can beselected from the second codebook C₂ ⁽²⁾.

In the case of rank 2 or higher, one of precoding matrices including aprecoding matrix set can be selected as in the case of rank 1. Here, aprecoding matrix can be composed of a precoding vector applied perlayer. In addition, W_1 is configured as described above and a precodingvector applied per layer can be selected from precoding vectors includedin W_1. That is, in the case of rank 2 or higher, a precoding vector setmay correspond to a precoding matrix set in the case of rank 1. Inaddition, a precoding matrix composed of a precoding vector selected perlayer can be derived. Accordingly, in the case of rank 2 or higher, aprecoding matrix set may refer to a set of precoding matrices generatedaccording to various combinations of precoding vectors for respectivelayers.

In an embodiment of the present invention, W_2 may be configured asrepresented by Equation 30.

$\begin{matrix}{\mspace{76mu} {{C_{2}^{(2)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{\phi \; Y_{1}} & {{- \phi}\; Y_{2}}\end{bmatrix}} \right\}}{{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{1},e_{2}} \right),\left( {e_{2},e_{3}} \right),\left( {e_{1},e_{4}} \right),\left( {e_{2},e_{4}} \right)} \right\}},{\phi \in \left\{ {1,j} \right\}}}}} & \left\lbrack {{Equation}\mspace{14mu} 30} \right\rbrack\end{matrix}$

As represented by Equation 30, L_2 is 4 bits since L_2S=3 and L_2C=1.

In the case of rank 2, α_(i), can also be introduced as in Equation 29,which can be represented by Equation 31.

$\begin{matrix}{\mspace{76mu} {{C_{2}^{(2)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{\alpha_{i}\varphi \; Y_{1}} & {{- \alpha_{i}}\varphi \; Y_{2}}\end{bmatrix}} \right\}}{{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{1},e_{2}} \right),\left( {e_{2},e_{3}} \right),\left( {e_{1},e_{4}} \right),\left( {e_{2},e_{4}} \right)} \right\}},{\varphi \in \left\{ {1,j} \right\}}}}} & \left\lbrack {{Equation}\mspace{14mu} 31} \right\rbrack\end{matrix}$

Equations 28 and 29 corresponding to rank 1 and Equations 30 and 31corresponding to rank 2 may be combined and used. According to morespecific embodiments, W_2 can be configured according to a combinationof Equations 28 and 30, a combination of Equations 29 and 31, acombination of Equations 29 and 30 or a combination of Equations 29 and31.

As in Equations 29 and 31, a codebook considering a specific rotationcoefficient α_(i) may be used when the codebook W_2 which will bedescribed below is configured.

Cases in which L_1=4 and L_2=4 have been described. However, when L_1 isextended to 5, 6, 7, 8 and 9 bits for fixed L_2=4, the above-describedpatterns (FIGS. 15 to 23) constituting W_1 can be easily extended andapplied. 32 beams illustrated in FIGS. 15 to 23 are determined by anoversampling factor and dimensionality of an antenna port. That is, atotal number of beams is B_(T)=N_(h)Q_(h)N_(v)Q_(v), the number ofcolumns corresponds to B_(h)=N_(h)Q_(h) which is the number of columnsof W_1H corresponding to a horizontal DFT matrix, and the number of rowcorresponds to B_(v)=N_(v)Q_(v) which is the number of columns of W_1Vcorresponding to a vertical DFT matrix. The number of L_1 bits accordingto oversampling can be arranged as shown in Table 6.

Table 6 shows the number of L_1 bits according to oversampling when L_2is 4 in (2,2,2,8) AAS.

TABLE 6 Q_(h) Number of L_1 bits 2 4 8 16 Q_(v) 2 4 5 6 4 4 5 6 7 8 5 67 8 16 6 7 8 9

When Equation 21 is generalized using the number of L_1 bits, Equation32 is obtained. That is, when the number of L_1 bits is determined/setas shown in Table 6, the W_1 configuration method proposed by thepresent invention can be generalized as represented by Equation 32.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{w_{m{({i_{1},0})}}\mspace{14mu} w_{m{({i_{1},1})}}\mspace{14mu} w_{m{({i_{1},2})}}\mspace{14mu} w_{m{({i_{1},3})}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{B_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{v}}}\end{bmatrix}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor},{{m\left( {i_{1},i_{2}} \right)} = {{{\left( {{2i_{1}} + i_{2}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}\text{/}2} \right\rfloor \mspace{14mu} {for}\mspace{14mu} i_{1}}} = 0}},1,,{2^{L_{1}} - 1},{i_{2} = 0},1,2,3,}} & \left\lbrack {{Equation}\mspace{14mu} 32} \right\rbrack\end{matrix}$

Furthermore, a legacy 4 Tx codebook of 3GPP release-12 may be used forthe horizontal part. In this case, Equation 32 can be modified intoEquation 33.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{w_{m{({i_{1},0})}}\mspace{14mu} w_{m{({i_{1},1})}}\mspace{14mu} w_{m{({i_{1},2})}}\mspace{14mu} w_{m{({i_{1},3})}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{B_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{v}}}\end{bmatrix}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor},{{m\left( {i_{1},i_{2}} \right)} = {{{\left( {i_{1} + {\mu \; i_{2}}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}\text{/}2} \right\rfloor \mspace{14mu} {for}\mspace{14mu} i_{1}}} = 0}},1,,{2^{L_{1}} - 1},{i_{2} = 0},1,2,3,}} & \left\lbrack {{Equation}\mspace{14mu} 33} \right\rbrack\end{matrix}$

Here, μ refers to the spacing between beams in the same W_1 group, andwhen μ=8, the horizontal direction is the same as that in the legacyrelease-12 4 Tx codebook.

Equations 22, 23, 24, 26 and 27 can be generalized by modifying thefunction m(i₁,i₂) in the generalized equation 32.

When the function m(i₁,i₂) in Equation 32 is modified into Equation 34,Equation 22 can be generalized.

$\begin{matrix}{{{m\left( {i_{1},i_{2}} \right)} = {{\left( {i_{1} + {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{h}} + {2B_{h}\left\lfloor \frac{i_{1}}{B_{h}} \right\rfloor} + {B_{h}\left\lfloor \frac{i_{2}}{2} \right\rfloor}}},{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,3.} & \left\lbrack {{Equation}\mspace{14mu} 34} \right\rbrack\end{matrix}$

In addition, when the function m(i₁,i₂) in Equation 32 is modified intoEquation 35, Equation 23 can be generalized.

$\begin{matrix}{{{m\left( {i_{1},i_{2}} \right)} = {{\left( {i_{1} + {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2}} \right)\mspace{14mu} {mod}\mspace{11mu} B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}} \right\rfloor} + {\mu \; B_{h}\left\lfloor \frac{i_{1}}{\mu \; B_{h}} \right\rfloor} + {B_{h}\mu \left\lfloor \frac{i_{2}}{2} \right\rfloor}}},{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,3.} & \left\lbrack {{Equation}\mspace{14mu} 35} \right\rbrack\end{matrix}$

Furthermore, when the function m(i₁,i₂) in Equation 32 is modified intoEquation 36, Equation 24 can be generalized.

$\begin{matrix}{{{m\left( {i_{1},i_{2}} \right)} = {\left( {{2i_{1}} + {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2} + {B_{h}\left\lfloor \frac{i_{1}}{2} \right\rfloor}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{T}}},{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,3.} & \left\lbrack {{Equation}\mspace{14mu} 36} \right\rbrack\end{matrix}$

Further, when the function m(i₁,i₂) in Equation 32 is modified intoEquation 37, Equation 26 can be generalized.

$\begin{matrix}{{{m\left( {i_{1},i_{2}} \right)} = {\left( {{\left( {i_{1} + {a \cdot \left( {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2} \right)}\; + {b\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\mspace{14mu} B_{h}} + {{2 \cdot B_{h}}\; \left\lfloor \frac{i_{1}}{B_{h}} \right\rfloor} + {{B_{h} \cdot c}\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\mspace{14mu} B_{T}}},{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,3.} & \left\lbrack {{Equation}\mspace{14mu} 37} \right\rbrack\end{matrix}$

In addition, when the function m(i₁,i₂) in Equation 32 is modified intoEquation 38, Equation 27 can be generalized.

$\begin{matrix}{{{m\left( {i_{1},i_{2}} \right)} = {\left( {{\left( {{2i_{1}} + {a \cdot \left( {i_{2}\mspace{14mu} {mod}\mspace{14mu} 2} \right)}\; + {b\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\mspace{14mu} B_{h}} + {B_{h}\; \left\lfloor \frac{i_{1}}{B_{h}\text{/}2} \right\rfloor} + {{B_{h} \cdot c}\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\mspace{14mu} B_{T}}},{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,3.} & \left\lbrack {{Equation}\mspace{14mu} 38} \right\rbrack\end{matrix}$

Furthermore, the indexes of columns constituting W_1 may be grouped intoa set in the vertical direction instead of the horizontal direction inEquation 32. This can be represented by Equation 39.

$\begin{matrix}{{{m\left( {i_{1},i_{2}} \right)} = {\left( {i_{1} + {B_{h}i_{2}} + \left\lfloor \frac{i_{1}}{B_{h}} \right\rfloor} \right)\mspace{14mu} {mod}\mspace{14mu} B_{T}}},{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,3.} & \left\lbrack {{Equation}\mspace{14mu} 39} \right\rbrack\end{matrix}$

In another embodiment in which W_1 is composed of 4 vectors, W_1 may beconfigured as represented by Equation 40.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{w_{{(i_{1})}{mod}\; 32}\mspace{14mu} w_{{({i_{1} + 9})}{mod}\; 32}\mspace{14mu} w_{{({i_{1} + 18})}{mod}\; 32}\mspace{14mu} w_{{({i_{1} + 27})}{mod}\; 32}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 8}},{v = \left\lfloor \frac{m}{8} \right\rfloor},{m \in \left\{ \left( {i_{1} + {9i_{2}}} \right) \right\}},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 40} \right\rbrack\end{matrix}$

Equation 40 is represented as the diagram of FIG. 24.

FIG. 24 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 24, W_1 can be configured in a back slash pattern. Inthe case of the back slash pattern as shown in FIG. 24, a spacing ofbeams constituting W_1 can be set to 9.

When the W_1 configuration method as shown in FIG. 24 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y+1), (x+2,y+2) and (x+3,y+3). Here, x and y are integers that arenot negative numbers.

In addition, the spacing of beams constituting W_1 is set to 8, avertical stripe pattern can be configured.

m(i₁,i₂) in Equation 40 can be generalized by being modified intoEquation 41.

m(i ₁ ,i ₂)=(i ₁ +μi ₂)mod B _(T), for i ₁=0,1, . . . ,2^(L) ¹ −1, i₂=0,1,2,3.  [Equation 41]

Here, μ indicates a uniform spacing between beam vectors constitutingW_1, i_1 indicates the index of W_1, and i_2 is an index correspondingto selection of W_2.

When W_1 is configured as illustrated in FIGS. 17 and 21 (or FIGS. 22and 23), W_1 can be configured by consecutively arranging the indexes ofbeams in the horizontal or vertical direction or setting a gap.

Furthermore, there are Equations 32 and 33 in which only horizontalbeams are configured in a given vertical domain. Horizontallyconsecutive beams constitute W_1 in the case of Equation 32 and beamshaving a spacing of 8 in the horizontal direction constitute W_1 in thecase of Equation 33.

Such codebook configuration methods can be adaptively applied accordingto BS antenna layout. That is, when antenna port layout is wide in thehorizontal direction (e.g., a TXRU subarray model or the like), Equation33 which represents a case in which the beam spacing in W_1 is wide canbe used or the parameters for determining a horizontal spacing in FIG.21 (or FIGS. 22 and 23) can be set to determine a wider spacing.

On the contrary, when horizontal antenna port layout is narrow, Equation32 can be used or the parameters for determining a horizontal spacing inFIG. 21 (or FIGS. 22 and 23) can be set to determine a narrower spacing.The same applies to a vertical case. Furthermore, antenna port layoutcan be adaptively set using the parameters for determining a beamspacing in FIGS. 17 and 21 (or FIGS. 22 and 23) according to granularityof vertical or horizontal beams.

Cases in which the number of feedback bits of long-term W_1 is increasedin a 2D AAS have been described. This is more advantageous than a casein which the number of feedback bits of short-term W_2 is increased interms of system overhead. However, a case in which the number of bits ofW_2 is increased may also be considered in a 2D AAS using large antennaports.

As another embodiment of the present invention, a method of configuringa codebook for the 8 TXRU 2D AAS as shown in FIG. 14(a) will bedescribed. A case in which Q_(h)=16, Q_(v)=4, L₁=6 is assumed.

In this case, the number of columns constituting the entire codebook C_1is 256 (=N_(h)Q_(h)N_(v)Q_(v)=2*16*2*4). In addition, each column iscomposed of a 4 Tx DFT vector.

Among the columns of C_1, W_1 may be considered to be composed of 8 DFTvectors (i.e., 8 columns) according to i_1. In this case, variouspatterns constituting W1 can also be considered similarly to a case inwhich L_2=4.

In an embodiment according to the present invention, W_1 may beconfigured as represented by Equation 42.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{{({{4i_{1}} + 0})}{mod}\; 32} + {32{\lfloor\frac{i_{1}}{8}\rfloor}}}\mspace{14mu} w_{{{({{4i_{1}} + 1})}{mod}\; 32} + {32{\lfloor\frac{i_{1}}{8}\rfloor}}}\mspace{14mu} \cdots \mspace{14mu} w_{{{({{4i_{1}} + 7})}{mod}\; 32} + {32{\lfloor\frac{i_{1}}{8}\rfloor}}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{32}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{16}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 32}},{v = \left\lfloor \frac{m}{32} \right\rfloor},{m \in \left\{ {{\left( {{4i_{1}} + i_{2}} \right){mod}\; 32} + {32\left\lfloor \frac{i_{1}}{8} \right\rfloor}} \right\}},{i_{1} = 0},1,\ldots,63,{i_{2} = 0},1,2,\ldots,7}} & \left\lbrack {{Equation}\mspace{14mu} 42} \right\rbrack\end{matrix}$

Equation 42 is represented as the diagram of FIG. 25.

FIG. 25 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

In FIG. 25, numerals 0 to 255 indicate indexes of columns constitutingthe entire codebook C_1, and h and v respectively indicate a horizontalcomponent and a vertical component of a DFT vector constituting w_m inW_1 which is an element of C_1.

Referring to FIG. 25, W_1 is composed of 8 columns, and 4 beams mayoverlap between W_1s having adjacent indexes i_1.

When the W_1 configuration method as shown in FIG. 25 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x+2,y), (x+3,y), (x+4,y), (x+5,y), (x+6,y) and (x+7,y). Here,x and y are integers that are not negative numbers.

When Equation 42 is generalized into Equation 43.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{{({{4i_{1}} + 0})}{mod}\; B_{h}} + {B_{h}{\lfloor\frac{i_{1}}{B_{h}\text{/}4}\rfloor}}}\mspace{14mu} w_{{{({{4i_{1}} + 1})}{mod}\; B_{h}} + {B_{h}{\lfloor\frac{i_{1}}{B_{h}\text{/}4}\rfloor}}}\mspace{14mu} \cdots \mspace{14mu} w_{{{({{4i_{1}} + 7})}{mod}\; B_{h}} + {B_{h}{\lfloor\frac{i_{1}}{B_{h}\text{/}4}\rfloor}}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{B_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{v}}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 32}},{v = \left\lfloor \frac{m}{B_{h}} \right\rfloor},{m \in \left\{ {{\left( {{4i_{1}} + i_{2}} \right){mod}\; B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}\text{/}4} \right\rfloor}} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,\ldots,7}} & \left\lbrack {{Equation}\mspace{14mu} 43} \right\rbrack\end{matrix}$

As another embodiment, W_1 may be configured as represented by Equation44.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{{({{2i_{1}} + 0})}{mod}\; B_{h}} + {{2 \cdot B_{h}}{\lfloor\frac{i_{1}}{B_{h}\text{/}2}\rfloor}}}\mspace{14mu} w_{{{({{2i_{1}} + 1})}{mod}\; B_{h}} + {{2 \cdot B_{h}}{\lfloor\frac{i_{1}}{B_{h}\text{/}2}\rfloor}}}\mspace{14mu} \cdots \mspace{14mu} w_{{{({{2i_{1}} + 3})}{mod}\; B_{h}} + {{2 \cdot B_{h}}{\lfloor\frac{i_{1}}{B_{h}\text{/}2}\rfloor}} + B_{h}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{B_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{v}}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} 32}},{v = \left\lfloor \frac{m}{B_{h}} \right\rfloor},{m \in \left\{ {{\left( {{2i_{1}} + {i_{2}\mspace{14mu} {mod}\mspace{14mu} 4}} \right){mod}\; B_{h}} + {{2 \cdot B_{h}}\left\lfloor \frac{i_{1}}{B_{h}\text{/}2} \right\rfloor} + {B_{h}\left\lfloor \frac{i_{2}}{4} \right\rfloor}} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,\ldots,7}} & \left\lbrack {{Equation}\mspace{14mu} 44} \right\rbrack\end{matrix}$

Equation 44 is represented as the diagram of FIG. 26.

FIG. 26 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 26, W_1 is composed of 4 horizontal elements and 2vertical elements, and 2 horizontal elements may overlap between W_1shaving adjacent indexes i_1.

When the W_1 configuration method as shown in FIG. 26 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x+2,y), (x+3,y), (x,y+1), (x+1,y+1), (x+2,y+1) and (x+3,y+1).Here, x and y are integers that are not negative numbers.

As another embodiment, W_1 may be configured as represented by Equation45.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{({4i_{1}})}{mod}\; B_{T}}\mspace{14mu} w_{{({{4i_{1}} + 1})}{mod}\; B_{T}}\mspace{14mu} \cdots \mspace{14mu} w_{{({{4i_{1}} + 3 + B_{h}})}{mod}\; B_{T}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{B_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{v}}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m}{B_{h}} \right\rfloor},{m \in \left\{ {\left( {{4i_{1}} + {i_{2}\mspace{11mu} {mod}\; 4} + \; {B_{h}\left\lfloor \frac{i_{2}}{4} \right\rfloor}} \right){mod}\mspace{14mu} B_{T}} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,\ldots,7}} & \left\lbrack {{Equation}\mspace{14mu} 45} \right\rbrack\end{matrix}$

Here, i_1 indicates the index of W_1 and i_2 is an index correspondingto selection of W_2. B_h indicates the product of the number ofhorizontal antenna ports and the oversampling factor and B_v indicatesthe product of the number of vertical antenna ports and the oversamplingfactor.

Equation 45 is represented as the diagram of FIG. 27.

FIG. 27 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 27, W_1 is composed of 4 horizontal elements and 2vertical elements, and one horizontal element may overlap between W_1shaving adjacent indexes i_1.

When the W_1 configuration method as shown in FIG. 27 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x+2,y), (x+3,y), (x,y+1), (x+1,y+1), (x+2,y+1) and (x+3,y+1).Here, x and y are integers that are not negative numbers.

As another embodiment, W_1 may be configured as represented by Equation46.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{({2i_{1}})}{mod}\; B_{T}}\mspace{14mu} w_{{({{2i_{1}} + 1})}{mod}\; B_{T}}\mspace{14mu} \cdots \mspace{14mu} w_{{({{2i_{1}} + 1 + {3B_{h}}})}{mod}\; B_{T}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{B_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{v}}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m}{B_{h}} \right\rfloor},{m \in \left\{ {\left( {{2i_{1}} + {i_{2}\mspace{11mu} {mod}\; 2} + \; {B_{h}\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\mspace{14mu} B_{T}} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,\ldots,7}} & \left\lbrack {{Equation}\mspace{14mu} 46} \right\rbrack\end{matrix}$

Here, i_1 indicates the index of W_1 and i_2 is an index correspondingto selection of W_2. B_h indicates the product of the number ofhorizontal antenna ports and the oversampling factor and B_v indicatesthe product of the number of vertical antenna ports and the oversamplingfactor.

Equation 46 is represented as the diagram of FIG. 28.

FIG. 28 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 28, W_1 is composed of 2 horizontal elements and 4vertical elements, and 2 horizontal element may overlap between W_1shaving adjacent indexes i_1.

When the W_1 configuration method as shown in FIG. 28 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x,y+1), (x+1,y+1), (x,y+2), (x+1,y+2), (x,y+3) and (x+1,y+3).Here, x and y are integers that are not negative numbers.

As another embodiment, W_1 may be configured as represented by Equation47.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{({{i_{1}{mod}\; B_{h}} + {{2 \cdot B_{h}}{\lfloor\frac{i_{2}}{B_{h}}\rfloor}}})}{mod}\; B_{T}}\mspace{14mu} w_{{({{{({i_{1} + 1})}{mod}\; B_{h}} + B_{h} + {{2 \cdot 2}B_{h}{\lfloor\frac{i_{1}}{B_{h}}\rfloor}}})}{mod}\; B_{T}}\mspace{14mu} \cdots \mspace{14mu} w_{{({{{({i_{1} + 3})}{mod}\; B_{h}} + {3B_{h}} + {2B_{h}{\lfloor\frac{i_{2}}{B_{h}}\rfloor}}})}{mod}\; B_{T}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{B_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{v}}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m}{B_{h}} \right\rfloor},{m \in \left\{ {\left( {{\left( {i_{1} + \left( {i_{2}\mspace{11mu} {mod}\; 4} \right)} \right){mod}\; B_{h}} + \; {B_{h}\left( {i_{2}\mspace{14mu} {mod}\; 2} \right)} + {2{B_{h}\left( {\left\lfloor \frac{i_{1}}{B_{h}} \right\rfloor + \left\lfloor \frac{i_{2}}{4} \right\rfloor} \right)}}} \right){mod}\mspace{14mu} B_{T}} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,\ldots,7}} & \left\lbrack {{Equation}\mspace{14mu} 47} \right\rbrack\end{matrix}$

In the above configuration method, B_(k) W_1s are present in thehorizontal direction and B_(v)/2 W_1 groups are present in the verticaldirection. Similarly, a codebook may be generated by arranging B_(k)/2W_1s in the horizontal direction and arranging B_(v)4 W_1 groups in thevertical direction. This can be represented by Equation 48.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{({{2i_{1}{mod}\; B_{h}} + {{2 \cdot B_{h}}{\lfloor\frac{i_{2}}{B_{h}}\rfloor}}})}{mod}\; B_{T}}\mspace{14mu} w_{{({{{({{2i_{1}} + 1})}{mod}\; B_{h}} + B_{h} + {2B_{h}{\lfloor\frac{i_{1}}{B_{h}}\rfloor}}})}{mod}\; B_{T}}\mspace{14mu} \cdots \mspace{14mu} w_{{({{{({i_{1} + 3})}{mod}\; B_{h}} + {3B_{h}} + {B_{h}{\lfloor\frac{i_{2}}{B_{h}}\rfloor}}})}{mod}\; B_{T}}} \right\rbrack} \right\}}{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{B_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{v}}}\end{bmatrix}},{h = {m\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m}{B_{h}} \right\rfloor},{m \in \left\{ {\left( {{\left( {{2i_{1}} + \left( {i_{2}\mspace{11mu} {mod}\; 4} \right)} \right){mod}\; B_{h}} + \; {B_{h}\left( {i_{2}\mspace{14mu} {mod}\; 2} \right)} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}} \right\rfloor} + {2B_{h}\left\lfloor \frac{i_{2}}{4} \right\rfloor}} \right){mod}\mspace{14mu} B_{T}} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},,{i_{2} = 0},1,2,\ldots,7} & \left\lbrack {{Equation}\mspace{14mu} 48} \right\rbrack\end{matrix}$

Equation 47 is represented as the diagram of FIG. 29.

FIG. 29 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 29, 8 beam vectors constituting W_1 among columnindexes belonging to a 4×4 square can be selected in a check pattern.This is generalized by Equation 47.

When the W_1 configuration method as shown in FIG. 29 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y+1), (x+2,y), (x+3,y+1), (x,y+2), (x+1,y+3), (x+2,y+2) and(x+3,y+3). Here, x and y are integers that are not negative numbers.

When W_1 is configured using Equations 42 to 48, W_2 is configuredthrough the following method.

In the case of transmission rank 1, the outer precoder W₂ can beselected from the second codebook C₂ ⁽¹⁾.

As an embodiment according to the present invention, W_2 can beconfigured as represented by Equation 49.

$\begin{matrix}{{C_{2}^{(1)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{\phi \; Y}\end{bmatrix}} \right\}},{Y \in \left\{ {e_{1},e_{2},e_{3},r_{4},e_{5},e_{6},e_{7},e_{8}} \right\}},{\phi \in {\left\{ {1,{- 1},j,{- j}} \right\}.}}} & \left\lbrack {{Equation}\mspace{14mu} 49} \right\rbrack\end{matrix}$

As represented in Equation 49, L_2 is 5 bits since L_2S=3 and L_2C=2

In the case of transmission rank 2, the outer precoder W₂ can beselected from the second codebook C₂ ⁽²⁾.

As an embodiment according to the present invention, W_2 can beconfigured as represented by Equation 50.

$\begin{matrix}{\mspace{76mu} {{C_{2}^{(2)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{\phi \; Y_{1}} & {{- \phi}\; Y_{2}}\end{bmatrix}} \right\}}{{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{5},e_{5}} \right),\left( {e_{6},e_{6}} \right),\left( {e_{7},e_{7}} \right),{\left( {e_{8},e_{8}} \right)\left( {e_{4},e_{5}} \right)},\left( {e_{3},e_{6}} \right),\left( {e_{3},e_{5}} \right),\left( {e_{1},e_{2}} \right),\left( {e_{2},e_{5}} \right),\left( {e_{4},e_{8}} \right),\left( {e_{5},e_{6}} \right),\left( {e_{3},e_{7}} \right)} \right\}},{\phi \in \left\{ {1,j} \right\}}}}} & \left\lbrack {{Equation}\mspace{14mu} 50} \right\rbrack\end{matrix}$

As represented in Equation 50, L_2 is 5 bits since L_2S=4 and L_2C=1

Here, combinations of selection vectors may be obtained through thefollowing methods.

1) A method of generating 8 pairs according to combinations of the samevectors and preferentially filling the remaining 8 pairs withcombinations of consecutive vectors

An example of this method as represented by Equation 51 can be provided.

(Y ₁ ,Y ₂)ϵ{(e ₁ ,e ₁),(e ₂ ,e ₂),(e ₃ ,e ₃),(e ₄ ,e ₄),(e ₅ ,e ₅),(e ₆,e ₆),(e ₇ ,e ₇),(e ₈ ,e ₈)(e ₁ ,e ₂),(e ₂ ,e ₃),(e ₃ ,e ₄),(e ₄ ,e₅),(e ₅ ,e ₆),(e ₆ ,e ₇),(e ₇ ,e ₈),(e ₁ ,e ₄)}, φϵ{1,j}  [Equation 51]

2) A method of configuring a combination of vectors such that a chordaldistance is maximized for all available pairs when a final codebook W iscalculated

Here, a chordal distance between matrices A and B is defined asrepresented by Equation 52.

$\begin{matrix}{{D\left( {A,B} \right)} = {\frac{1}{\sqrt{2}}{{{AA}^{H} - {BB}^{H}}}_{F}}} & \left\lbrack {{Equation}\mspace{14mu} 52} \right\rbrack\end{matrix}$

In Equation 52, ∥.∥_(F) refers to Frobenius norm operation. An exampleof this method can be represented by Equation 50.

3) 8 pairs are generated according to combinations of the same vectorsas represented by Equation 53 and 2-bit co-phasing is generated toproduce a total of 5 bits.

(Y ₁ ,Y ₂)ϵ{(e ₁ ,e ₁),(e ₂ ,e ₂),(e ₃ ,e ₃),(e ₄ ,e ₄),(e ₅ ,e ₅),(e ₆,e ₆),(e ₇ ,e ₇),(e ₈ ,e ₈)}, ϕϵ{1,j,−1,−j}  [Equation 53]

In addition, when L_2=6 bits are considered, W_2 configuration below canbe considered.

In the case of transmission rank 1, the outer precoder W₂ can beselected from the second codebook C₂ ⁽¹⁾.

As an embodiment according to the present invention, W_2 can beconfigured as represented by Equation 54.

$\begin{matrix}{{C_{2}^{(1)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{\phi \; Y}\end{bmatrix}} \right\}},{Y \in \left\{ {e_{1},e_{2},e_{3},e_{4},e_{5},e_{6},e_{7},e_{8}} \right\}},{\phi \in {\left\{ {1,{- 1},j,{- j},\frac{1 + j}{\sqrt{2}},\frac{1 - j}{\sqrt{2}},\frac{{- 1} + j}{\sqrt{2}},\frac{{- 1},{- j}}{\sqrt{2}}} \right\}.}}} & \left\lbrack {{Equation}\mspace{14mu} 54} \right\rbrack\end{matrix}$

As represented in Equation 54, L_2 is 6 bits since L_2S=3 and L_2C=3

In the case of transmission rank 2, the outer precoder W₂ can beselected from the second codebook C₂ ⁽²⁾.

As an embodiment according to the present invention, W_2 can beconfigured as represented by Equation 55.

$\begin{matrix}{\mspace{79mu} {{C_{2}^{(2)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{\phi \; Y_{1}} & {{- \phi}\; Y_{2}}\end{bmatrix}} \right\}}{{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{5},e_{5}} \right),\left( {e_{6},e_{6}} \right),\left( {e_{7},e_{7}} \right),{\left( {e_{8},e_{8}} \right)\left( {e_{4},e_{5}} \right)},\left( {e_{3},e_{6}} \right),\left( {e_{3},e_{5}} \right),\left( {e_{1},e_{2}} \right),\left( {e_{2},e_{5}} \right),\left( {e_{4},e_{8}} \right),\left( {e_{5},e_{6}} \right),\left( {e_{3},e_{7}} \right)} \right\}},\mspace{20mu} {\phi \in \left\{ {1,{- 1},j,{- j}} \right\}}}}} & \left\lbrack {{Equation}\mspace{14mu} 55} \right\rbrack\end{matrix}$

As represented in Equation 55, L_2 is 6 bits since L_2S=4 and L_2C=2

As another embodiment according to the present invention, W_2 can beconfigured as represented by Equation 56.

$\begin{matrix}{\mspace{79mu} {{C_{2}^{(2)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{\phi \; Y_{1}} & {{- \phi}\; Y_{2}}\end{bmatrix}} \right\}}{{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{5},e_{5}} \right),\left( {e_{6},e_{6}} \right),\left( {e_{7},e_{7}} \right),{\left( {e_{8},e_{8}} \right)\left( {e_{1},e_{2}} \right)},\left( {e_{2},e_{3}} \right),\left( {e_{3},e_{4}} \right),\left( {e_{4},e_{5}} \right),\left( {e_{5},e_{6}} \right),\left( {e_{6},e_{7}} \right),\left( {e_{7},e_{8}} \right),{\left( {e_{1},e_{3}} \right)\left( {e_{1},e_{4}} \right)},\left( {e_{1},e_{5}} \right),\left( {e_{1},e_{6}} \right),\left( {e_{1},e_{7}} \right),\left( {e_{1},e_{8}} \right),\left( {e_{2},e_{4}} \right),\left( {e_{2},e_{5}} \right),{\left( {e_{2},e_{6}} \right)\left( {e_{2},e_{7}} \right)},\left( {e_{2},e_{8}} \right),\left( {e_{3},e_{5}} \right),\left( {e_{3},e_{6}} \right),\left( {e_{3},e_{7}} \right),\left( {e_{3},e_{8}} \right),\left( {e_{4},e_{6}} \right),\left( {e_{4},e_{7}} \right)} \right\}},\mspace{20mu} {\phi \in \left\{ {1,j} \right\}}}}} & \left\lbrack {{Equation}\mspace{14mu} 56} \right\rbrack\end{matrix}$

As represented in Equation 56, L_2 is 6 bits since L_2S=5 and L_2C=1.

The method of determining (Y_1, Y_2) pair described with reference toEquation 50 can be equally applied to Equations 55 and 56.

2. 12 TXRU

Methods of configuring a codebook for a 12 TXRU 2D AAS as shown in FIG.14(b) will be described. In the case of 12 TXRU as shown in FIG. 14(b),two cases of (3,2,2,12) and (2,3,2,12) can be considered according to 2Dantenna panel form.

Although the case of (2,3,2,12) will be described, the present inventionis not limited thereto and a codebook can be extended and applied in thecase of (3,2,2,12) similarly to the (2,3,2,12) codebook design methodwhich will be described below.

First, a case in which Q_(h)=2, Q_(v)=2, L₁=4 is assumed.

In this case, since there are 3 Tx antenna ports in the horizontaldirection and 2 Tx antenna ports in the vertical direction, columnsconstituting final W_1 are composed of 6 Tx DFT vectors and thestructure is represented by Equation 57.

$\begin{matrix}{{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{3\; Q_{h}}} \\e^{j\frac{4\pi \; h}{3\; Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{2\; Q_{v}}}\end{bmatrix}},{v_{m} = {v_{h} \otimes v_{v}}}} & \left\lbrack {{Equation}\mspace{14mu} 57} \right\rbrack\end{matrix}$

Here, m is a function of i_1 and i_2 as in the case of 8 TXRU.

First, a case in which the number of columns (i.e., the number of beams)constituting W_1 is selected as 4 in the entire codebook C_1, as in thecase of 8 TXRU, can be considered.

As an embodiment according to the present invention, W_1 can beconfigured as represented by Equation 58.

$\begin{matrix}{{C_{1} = \begin{Bmatrix}\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \right| \\{{\overset{\sim}{W}}_{1} = {\quad\left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{\begin{matrix}w_{m{({i_{1},0})}} & w_{m{({i_{1},1})}} & w_{m{({i_{1},2})}} & w_{m{({i_{1},3})}}\end{matrix}} \right\rbrack}}\end{Bmatrix}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{3\; Q_{h}}} \\e^{j\frac{4\pi \; h}{3\; Q_{h}}}\end{bmatrix}},,{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{h}}}\end{bmatrix}},\mspace{20mu} {h = {{m\left( {i_{1},i_{2}} \right)}{mod}\; B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor},\mspace{20mu} {{m\left( {i_{1},i_{2}} \right)} = {{\left( {{2\; i_{1}} + i_{2}} \right){mod}\; B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}/2} \right\rfloor}}}}\mspace{20mu} {{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots \mspace{14mu},{2^{L_{1}} - 1},{i_{2} = 0},1,2,3,}} & \left\lbrack {{Equation}\mspace{14mu} 58} \right\rbrack\end{matrix}$

Equation 58 represented as the diagram of FIG. 30.

FIG. 30 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 30, since the number of columns is not an exponent of2, 3 W_1s can be configured for a fixed vertical index and thus a totalof 12 W_1s can be configured.

When the W_1 configuration method as shown in FIG. 30 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x+2,y) and (x+3,y). Here, x and y are integers that are notnegative numbers.

A total number of W_1s which can be configured using L_1=4 is 16. Here,a case in which only 12 W_1s are used and a case in which 16 W_1s areused can be considered.

1) When only 12 W_1s are used

W_1 can be configured using Equation 32.

If 12, 13, 14 and 15 are obtained as a result of decoding (by a BS)feedback information (of a UE) about W_1, it can be determined (by theBS) that error has been generated with respect to W_1.

When reserved states (e.g., 12, 13, 14 and 15 in the above-describedexample) are present in a specific reporting type such as W_1 feedback,the present invention causes a receiving end to perform error checkusing the reserved states. Accordingly, the present invention proposestechniques for preventing following feedback instances from becoming ameaningless report due to corresponding error. For example, at least oneof the following methods can be applied.

1-A) A BS can transmit an aperiodic CSI request signal/message to a UEto receive CSI including W_1 through aperiodic feedback.

1-B) When a periodic feedback chain is used, the BS can ignore all ofreceived CSI (e.g., CSI having lower feedback levels or short periodswith respect to W_1, for example, X_2 and/or CQI) until W_1 having anerror is reported in the next period.

1-C) When a periodic feedback chain is used, the BS can signal (e.g.,through DCI) a specific B-bit indicator (e.g., B=1) in #n subframe (SF)to override a reporting type (e.g., W_1) (having an error) such that thereporting type is exceptionally retransmitted.

Here, it is possible to override the reporting type (e.g., W_1) (havingan error) for a CSI process of feeding back the most recently reportedspecific reporting type (e.g., W_1) before #(n−k) SF (e.g., k can bepredefined or configured for a UE) according to the B-bit indicator toexceptionally retransmit the reporting type. Additionally/alternatively,when a specific X port (e.g., X=12) CSI report including the reservedstates is set in the CSI process, it is possible to override thereporting type (having an error) (e.g., W_1) at periodic reportinginstance(s) that initially appear after #n SF of the CSI process toexceptionally retransmit the reporting type.

Furthermore, to prevent unnecessary uplink overhead, a UE may be definedor configured to drop (i.e., not to transmit) other pieces of CSI (e.g.,CSI having lower feedback levels or short periods with respect to W_1,for example, X_2 and/or CQI) until a CSI reporting instance of the nextvalid reporting type (having an error) (e.g., W_1) appears.

By supporting such operations, it is possible to prevent unnecessaryuplink overhead for periodic consecutive CSI reporting instancesfollowing a specific periodic CSI reporting instance in which an erroris detected or to immediately indicate retransmission of CSI report toperform effective periodic reporting.

2) When 16 W_1s are used

When a method of additionally adding 4 W_1 configuration patterns isrepresented as a generalized equation, Equation 59 is obtained.

$\begin{matrix}{{C_{1} = \begin{Bmatrix}\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \right| \\{{\overset{\sim}{W}}_{1} = {\quad\left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{\begin{matrix}w_{m{({i_{1},0})}} & w_{m{({i_{1},1})}} & w_{m{({i_{1},2})}} & w_{m{({i_{1},3})}}\end{matrix}} \right\rbrack}}\end{Bmatrix}}\mspace{20mu} {{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{B_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{B_{v}}}\end{bmatrix}},\mspace{20mu} {h = {m\left( {i_{1},i_{2}} \right){mod}\; B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor},\left\{ \begin{matrix}{{m\left( {i_{1},i_{2}} \right)} = {{\left( {{2\; i_{1}} + i_{2}} \right){mod}\; B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}/2} \right\rfloor}}} & \begin{matrix}{{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots \mspace{14mu},{\frac{B_{h}B_{v}}{2} - 1},} \\{{i_{2} = 0},1,2,3,}\end{matrix} \\{{m\left( {i_{1},i_{2}} \right)} = {i_{1} - \frac{B_{h}B_{v}}{2} + {i_{2}B_{h}}}} & \begin{matrix}{{{{for}\mspace{14mu} i_{1}} = \frac{B_{h}B_{v}}{2}},\ldots \mspace{14mu},{2^{L_{1}} - 1},} \\{{i_{2} = 0},1,2,3,}\end{matrix}\end{matrix} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 59} \right\rbrack\end{matrix}$

Here, i_1 indicates the index of W_1 and i_2 is an index correspondingto selection of W_2. B_h indicates the product of the number ofhorizontal antenna ports and the oversampling factor and B_v indicatesthe product of the number of vertical antenna ports and the oversamplingfactor.

Equation 59 is represented as the diagram of FIG. 31.

FIG. 31 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

FIG. 31 illustrates a case in which a vertical pattern is consideredwhen i_1=12,13,14 and 15 in Equation 59.

As another embodiment, the patterns of FIGS. 18 to 21 (or FIGS. 22 and23) may be applied.

Since the number of columns constituting W_1 is 4, W_2 can be configuredusing Equations 28 or 30 when L_2=4.

Although L_1=4 and a case of using Equation 28 is described in theabove-described example, the present invention is not limited theretoand the above-described method can be easily extended and applied usingEquations 32 to 39 for all cases shown in Table 6.

Next, a case in which the number of columns (i.e., the number of beams)constituting W_1 is 6 may be considered.

As an embodiment according to the present invention, W_1 can beconfigured as represented by Equation 60.

$\begin{matrix}{{C_{1} = \begin{Bmatrix}\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \right| \\{{\overset{\sim}{W}}_{1} = {\quad\left\lbrack \underset{\underset{6\mspace{14mu} {columns}}{}}{\begin{matrix}w_{m{({i_{1},0})}} & w_{m{({i_{1},1})}} & w_{m{({i_{1},2})}} & w_{m{({i_{1},3})}} & w_{m{({i_{1},4})}} & w_{m{({i_{1},5})}}\end{matrix}} \right\rbrack}}\end{Bmatrix}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{3\; Q_{h}}} \\e^{j\frac{4\pi \; h}{3\; Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{2\; Q_{v}}}\end{bmatrix}},{h = {m\left( {i_{1},i_{2}} \right){mod}\; B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor},{{m\left( {i_{1},i_{2}} \right)} = {{\left( {{3\; i_{1}} + i_{2}} \right){mod}\; B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}/3} \right\rfloor}}}}{{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots \mspace{14mu},{2^{L_{1}} - 1},{i_{2} = 0},1,2,3,4,5}} & \left\lbrack {{Equation}\mspace{14mu} 60} \right\rbrack\end{matrix}$

Equation 60 is represented as the diagram of FIG. 32.

FIG. 32 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 32, indexes of columns constituting W_1 areconsecutive in the horizontal direction for given vertical elementindexes.

When the W_1 configuration method as shown in FIG. 32 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x+2,y), (x+3,y), (x+4,y) and (x+5,y). Here, x and y areintegers that are not negative numbers.

As another embodiment, W_1 can be configured by modifying the functionm(i₁,i₂) in Equation 60 into Equation 61.

$\begin{matrix}{{{m\left( {i_{1},i_{2}} \right)} = {{\left( {{3\; i_{1}} + \left( {i_{2}{mod}\; 3} \right)} \right){mod}\; B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}/3} \right\rfloor} + {B_{h}\left\lfloor \frac{i_{2}}{3} \right\rfloor}}}\mspace{20mu} {{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots \mspace{14mu},{2^{L_{1}} - 1},{i_{2} = 0},1,2,3,4,5}} & \left\lbrack {{Equation}\mspace{14mu} 61} \right\rbrack\end{matrix}$

Equation 60 to which the function m(i₁,i₂) in Equation 61 has beenapplied is represented as the diagram of FIG. 33.

FIG. 33 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 33, W_1 can be configured in a rectangular patterncomposed of a DFT vector having 3 horizontal elements and 2 verticalelements. In this case, 3 beams overlap between vertically adjacentW_1s.

When the W_1 configuration method as shown in FIG. 33 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x+2,y), (x,y+1), (x+1,y+1) and (x+2,y+1). Here, x and y areintegers that are not negative numbers.

In addition to the examples of FIGS. 32 and 33, a case in which twobeams overlap between W_1s may be considered. However, in the case of 12TXRU, the index of W1 cannot be represented as an exponent of 2, andthus all indexes cannot be used as in the above-described case in whichW_1 is composed of 4 beams.

This can be represented by Equation 62. W_1 can be configured bymodifying the function m(i₁,i₂) in Equation 59 into Equation 62.

$\begin{matrix}{{{m\left( {i_{1},i_{2}} \right)} = {{\left( {{2\; i_{1}} + \left( {i_{2}{mod}\; 3} \right)} \right){mod}\; B_{h}} + {2\; B_{h}\left\lfloor \frac{i_{1}}{B_{h}/2} \right\rfloor} + {B_{h}\left\lfloor \frac{i_{2}}{3} \right\rfloor}}}\mspace{20mu} {{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots \mspace{14mu},{2^{L_{1}} - 1},{i_{2} = 0},1,2,3,4,5}} & \left\lbrack {{Equation}\mspace{14mu} 62} \right\rbrack\end{matrix}$

Equation 62 is represented as the diagram of FIG. 34.

FIG. 34 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

When the W_1 configuration method as shown in FIG. 34 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x+2,y), (x,y+1), (x+1,y+1) and (x+2,y+1). Here, x and y areintegers that are not negative numbers.

In addition, W_1 can be configured by modifying the function m(i₁,i₂) inEquation 59 into Equation 63.

$\begin{matrix}{{{m\left( {i_{1},i_{2}} \right)} = {{\left( {{3\; i_{1}} + \left( {i_{2}{mod}\; 3} \right)} \right){mod}\; B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}/3} \right\rfloor} + {B_{h}\left\lfloor \frac{i_{2}}{3} \right\rfloor}}}\mspace{20mu} {{{{for}\mspace{14mu} i_{1}} = 0},1,\ldots \mspace{14mu},{2^{L_{1}} - 1},{i_{2} = 0},1,2,3,4,5}} & \left\lbrack {{Equation}\mspace{14mu} 63} \right\rbrack\end{matrix}$

Here, i_1 indicates the index of W_1 and i_2 is an index correspondingto selection of W_2. B_h indicates the product of the number ofhorizontal antenna ports and the oversampling factor and B_v indicatesthe product of the number of vertical antenna ports and the oversamplingfactor.

Equation 63 is represented as the diagram of FIG. 35.

FIG. 35 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

When the W_1 configuration method as shown in FIG. 35 is generalized,pairs of indexes in the first dimension and indexes in the seconddimension of precoding matrices constituting W_1 correspond to (x,y),(x+1,y), (x,y+1), (x+1,y+1), (x,y+2) and (x+1,y+2). Here, x and y areintegers that are not negative numbers.

W_1 is composed of 6 columns using Equations 60 to 63, and W_2 isconfigured using the following methods.

In the case of transmission rank 1, the outer precoder W₂ can beselected from the second codebook C₂ ⁽¹⁾.

As an embodiment according to the present invention, W_2 can beconfigured as represented by Equation 64.

$\begin{matrix}{{C_{2}^{(1)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{\varphi \; Y}\end{bmatrix}} \right\}},{Y \in \left\{ {e_{1},e_{2},e_{3},e_{4},e_{5},e_{6}} \right\}},{\varphi \in {\left\{ {1,{- 1},j,{- j}} \right\}.}}} & \left\lbrack {{Equation}\mspace{14mu} 64} \right\rbrack\end{matrix}$

As represented in Equation 52, L_2 is 5 bits since L_2S=3 and L_2C=2.

In the case of transmission rank 2, the outer precoder W₂ can beselected from the second codebook C₂ ⁽²⁾.

As an embodiment according to the present invention, W_2 can beconfigured as represented by Equation 65.

$\begin{matrix}{\mspace{79mu} {{C_{2}^{(2)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{\varphi \; Y_{1}} & {{- \varphi}\; Y_{2}}\end{bmatrix}} \right\}}{{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{5},e_{5}} \right),\left( {e_{6},e_{6}} \right),\left( {e_{1},e_{2}} \right),{\left( {e_{2},e_{3}} \right)\left( {e_{3},e_{4}} \right)},\left( {e_{4},e_{5}} \right),\left( {e_{5},e_{6}} \right),\left( {e_{1},e_{3}} \right),\left( {e_{1},e_{4}} \right),\left( {e_{1},e_{5}} \right),\left( {e_{1},e_{7}} \right),\left( {e_{2},e_{4}} \right)} \right\}},\mspace{20mu} {\varphi \in \left\{ {1,j} \right\}}}}} & \left\lbrack {{Equation}\mspace{14mu} 65} \right\rbrack\end{matrix}$

As represented in Equation 65, L_2 is 5 bits since L_2S=4 and L_2C=1.

As represented in Equation 66, 3 bits in the case that beam pairs arecomposed of its own beams and 2-bit for co-phasing may be consideredwhen rank 2 is configured.

(Y ₁ ,Y ₂)ϵ{(e ₁ ,e ₁),(e ₂ ,e ₂),(e ₃ ,e ₃),(e ₄ ,e ₄),(e ₅ ,e ₅),(e ₆,e ₆)}, ϕϵ{1,j,−1,−j}  [Equation 66]

Equations 64 to 66 illustrate a case in which L_2=5 bits. A case inwhich L_2=6 bits will be described below.

In the case of transmission rank 1, the outer precoder W₂ can beselected from the second codebook C₂ ⁽¹⁾.

W_2 can be configured as represented by Equation 67.

$\begin{matrix}{\mspace{79mu} {{C_{2}^{(2)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{\varphi \; Y_{1}} & {{- \varphi}\; Y_{2}}\end{bmatrix}} \right\}}{{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{5},e_{5}} \right),\left( {e_{6},e_{6}} \right),\left( {e_{1},e_{2}} \right),{\left( {e_{2},e_{3}} \right)\left( {e_{3},e_{4}} \right)},\left( {e_{4},e_{5}} \right),\left( {e_{5},e_{6}} \right),\left( {e_{1},e_{3}} \right),\left( {e_{1},e_{4}} \right),\left( {e_{1},e_{5}} \right),\left( {e_{1},e_{7}} \right),\left( {e_{2},e_{4}} \right)} \right\}},\mspace{20mu} {\varphi \in \left\{ {1,{- 1},j,{- j}} \right\}}}}} & \left\lbrack {{Equation}\mspace{14mu} 68} \right\rbrack\end{matrix}$

As represented in Equation 54, L_2 is 6 bits since L_2S=3 and L_2C=3

In the case of transmission rank 2, the outer precoder W₂ can beselected from the second codebook C₂ ⁽²⁾.

W_2 can be configured as represented by Equation 68.

$\begin{matrix}{\mspace{79mu} {{C_{2}^{(2)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{\varphi \; Y_{1}} & {{- \varphi}\; Y_{2}}\end{bmatrix}} \right\}}{{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{5},e_{5}} \right),\left( {e_{6},e_{6}} \right),\left( {e_{1},e_{2}} \right),{\left( {e_{1},e_{3}} \right)\left( {e_{1},e_{4}} \right)},\left( {e_{1},e_{5}} \right),\left( {e_{1},e_{6}} \right),\left( {e_{2},e_{3}} \right),\left( {e_{2},e_{4}} \right),\left( {e_{2},e_{5}} \right),\left( {e_{2},e_{6}} \right),{\left( {e_{3},e_{4}} \right)\left( {e_{3},e_{5}} \right)},\left( {e_{3},e_{6}} \right),\left( {e_{4},e_{5}} \right),\left( {e_{4},e_{6}} \right),\left( {e_{5},e_{6}} \right)} \right\}},\mspace{20mu} {\varphi \in \left\{ {1,j} \right\}}}}} & \left\lbrack {{Equation}\mspace{14mu} 69} \right\rbrack\end{matrix}$

As represented in Equation 68, L_2 is 6 bits since L_2S=4 and L_2C=2

Alternatively, W_2 can be configured as represented by Equation 69.

$\begin{matrix}{\mspace{76mu} {{C_{2}^{(2)} = \left\{ {\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{\varphi \; Y_{1}} & {{- \varphi}\; Y_{2}}\end{bmatrix}} \right\}}{{\left( {Y_{1},Y_{2}} \right) \in \left\{ {\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{5},e_{5}} \right),\left( {e_{6},e_{6}} \right),\left( {e_{1},e_{2}} \right),{\left( {e_{1},e_{3}} \right)\left( {e_{1},e_{4}} \right)},\left( {e_{1},e_{5}} \right),\left( {e_{1},e_{6}} \right),\left( {e_{2},e_{3}} \right),\left( {e_{2},e_{4}} \right),\left( {e_{2},e_{5}} \right),\left( {e_{2},e_{6}} \right),{\left( {e_{3},e_{4}} \right)\left( {e_{3},e_{5}} \right)},\left( {e_{3},e_{6}} \right),\left( {e_{4},e_{5}} \right),\left( {e_{4},e_{6}} \right),\left( {e_{5},e_{6}} \right)} \right\}},{\varphi \in \left\{ {1,j} \right\}}}}} & \left\lbrack {{Equation}\mspace{14mu} 69} \right\rbrack\end{matrix}$

As represented in Equation 68, L_2 is 6 bits since L_2S=5 and L_2C=1.

In the cases of Equations 67 and 69, L_2S is composed of 3 bits and 5bits, and thus eight (Y_1, Y_2) pairs and thirty-two (Y_1, Y_2) pairscan be represented. However, as represented in Equations 67 and 69,there are six (Y_1, Y_2) pairs and twenty-one (Y_1, Y_2) pairs.Accordingly, when indexes indicating pairs other than the pairs of thiscase are fed back from a UE, the BS recognizes the feedback as atransmission error and may operate as follows.

2-A) The BS can transmit an aperiodic CSI request signal/message to areception UE to receive information of W_2 through aperiodic feedback.

2-B) When a periodic feedback chain is used, the BS can ignore receivedother specific CSI until W_2 having an error is reported in the nextperiod.

2-C) Alternatively, the proposed operation method described in 1-C canbe applied to W_2 having a error.

When a periodic feedback chain is used, the BS can signal (e.g., throughDCI) a specific B-bit indicator (e.g., B=1) in #n subframe (SF) tooverride W_2 (having an error) such that W_2 is exceptionallyretransmitted.

Here, it is possible to override W_2 (having an error) for a CSI processof feeding back the most recently reported W_2 before #(n−k) SF (e.g., kcan be predefined or configured for a UE) according to the B-bitindicator to exceptionally retransmit W_2. Additionally/alternatively,it is possible to override W_2 (having an error) at specific periodicreporting instance(s) that initially appear after #n SF of the CSIprocess to exceptionally retransmit W_2.

Furthermore, to prevent unnecessary uplink overhead, a UE may be definedor configured to drop (i.e., not to transmit) other pieces of CSI untila CSI reporting instance of the next W_2 (having an error) appears.

Since L_2S is 4 in Equation 55, (Y_1, Y_2) pairs can be selected usingthe methods described with reference to Equations 51 and 52.

Codebook design for (2,3,2,12) has been described. Codebook design maybe similarly extended and applied in the case of (3,2,2,12). Adifference therebetween is that 6 Tx DFT vectors corresponding tocolumns constituting final W_1 are configured as represented by Equation57.

$\begin{matrix}{{V_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{2Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{3Q_{v}}} \\e^{j\frac{4\pi \; v}{3Q_{v}}}\end{bmatrix}},{v_{m} = {v_{h} \otimes v_{v}}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor}} & \left\lbrack {{Equation}\mspace{14mu} 70} \right\rbrack\end{matrix}$

Here, m(i₁,i₂) is a function of i_1 and i_2 which are indexes of W_1 andW_2 and a function with respect to the aforementioned method ofconfiguring W_1. The above-described codebook design method for 12 TXRUcan be extended and applied using the function to configure a codebookW.

The methods of configuring a codebook with DFT vectors corresponding toa BS antenna port panel size have been described. That is, whenhorizontal elements are exemplified, (2,2,2,8) is composed of 2 Tx DFTvectors and (3,2,2,12) is composed of 3 Tx DFT vectors. However,codebooks applied to legacy LTE based systems have indexes such as 2, 4and 8 which are exponents of 2, and 3 and 6 Tx codebooks having indexesthat are not exponents of 2 are used, it is expected that complexity inreception UE implementation increases.

To solve this, the present invention proposes methods of configuring acodebook using a DFT vector composed of exponents of 2 in a 2D AAS usingantenna ports having indexes that are not exponents of 2 as horizontalor vertical components or horizontal and vertical components.

Equation 71 represents a 4Tx DFT codebook C_4Tx having an oversamplingfactor of Q_h.

$\begin{matrix}{C_{4{Tx}} = \begin{bmatrix}1 & 1 & 1 & 1 & 1 & 1 & \cdots & 1 \\1 & {\exp \left( \frac{j\; 2\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 4\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 6\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 8\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 10\pi}{4 \cdot Q_{h}} \right)} & \cdots & {\exp \left( \frac{j\; {2 \cdot \left( {{4 \cdot Q_{h}} - 1} \right)}\pi}{4 \cdot Q_{h}} \right)} \\1 & {\exp \left( \frac{j\; 4\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 8\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 12\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 16\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 20\pi}{4 \cdot Q_{h}} \right)} & \cdots & {\exp \left( \frac{j\; {2 \cdot 2 \cdot \left( {{4 \cdot Q_{h}} - 1} \right)}\pi}{4 \cdot Q_{h}} \right)} \\1 & {\exp \left( \frac{j\; 6\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 12\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 18\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 24\pi}{4 \cdot Q_{h}} \right)} & {\exp \left( \frac{j\; 30\pi}{4 \cdot Q_{h}} \right)} & \cdots & {\exp \left( \frac{j\; {2 \cdot 3 \cdot \left( {{4 \cdot Q_{h}} - 1} \right)}\pi}{4 \cdot Q_{h}} \right)}\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 71} \right\rbrack\end{matrix}$

Oversampling is used to increase beam granularity of a codebook and maybe implemented by configuring a matrix composed of first, second, thirdand fourth rows of a 4Q_(h)×4Q_(h) DFT matrix. A method of configuring aP Tx codebook having an antenna port P that is not an exponent of 2using such an oversampling DTF matrix is described below.

3-A) An exponent of 2 which is greater than and closest to P isobtained. That is, N which satisfies 2^(N-1)<P<2^(N) can be obtained.

3-B) A NQ×NQ DFT matrix can be configured using an oversampling factor Qprovided in the system.

3-C) A sub-matrix C_PTx composed of first to P-th rows and first toPQ-th columns of the aforementioned matrix can be calculated.

When the codebook is composed of antenna ports having horizontal andvertical components that do not correspond to exponents of 2, it ispossible to repeat the above-described process to configure anothercodebook C′_PTx and then obtain the Kronecker product of codebooks C_PTxand C′_PTx to configure the entire codebook.

3. 16 TXRU

A method of configuring a codebook for a 16 TXRU 2D AAS as shown in FIG.14(c) will be described. As illustrated in FIG. 14(c), (2,4,2,16) and(4,2,2,16) may be configured according to antenna configuration in thecase of 16 TXRU.

An 8 Tx DFT vector constituting codebook C_1 for W_1 is configured asrepresented by Equation 72 in the case of (2,4,2,16).

$\begin{matrix}{{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{4Q_{h}}} \\e^{j\frac{4\pi \; h}{4Q_{h}}} \\e^{j\frac{6\pi \; h}{4Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{2Q_{v}}}\end{bmatrix}},{v_{m} = {v_{h} \otimes v_{v}}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor}} & \left\lbrack {{Equation}\mspace{14mu} 72} \right\rbrack\end{matrix}$

In the case of (4,2,2,16), An 8 Tx DFT vector constituting codebook C_1for W_1 is configured as represented by Equation 73.

$\begin{matrix}{{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{2Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4Q_{v}}} \\e^{j\frac{4\pi \; v}{4Q_{v}}} \\e^{j\frac{6\pi \; v}{4Q_{v}}}\end{bmatrix}},{v_{m} = {v_{h} \otimes v_{v}}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor}} & \left\lbrack {{Equation}\mspace{14mu} 73} \right\rbrack\end{matrix}$

Here, m(i₁,i₂) is a function of i_1 and i_2 which are indexes of W_1 andW_2 and a function with respect to the aforementioned method ofconfiguring W_1.

In the case of 16 TXRU, m(i₁,i₂) can be configured by reusing thepattern used in the case of 8 TXRU. That is, when W_1 is composed of 4columns, W1 can be configured by combining Equations 32 to 39 andEquations 72 and 73.

For example, a codebook is configured using the pattern of FIG. 15 in asystem using (2,4,2,16), as represented by Equation 74.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{w_{m{({i_{1},0})}}\mspace{14mu} w_{m{({i_{1},1})}}\mspace{14mu} w_{m{({i_{1},2})}}\mspace{14mu} w_{m{({i_{1},3})}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} v_{h}} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{4Q_{h}}} \\e^{j\frac{4\pi \; h}{4Q_{h}}} \\e^{j\frac{6\pi \; h}{4Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{2Q_{v}}}\end{bmatrix}},{v_{m} = {v_{h} \otimes v_{v}}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = {\left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor.}}}} & \left\lbrack {{Equation}\mspace{14mu} 74} \right\rbrack\end{matrix}$

Here, i_1 indicates the index of W_1 and i_2 is an index correspondingto selection of W_2. B_h indicates the product of the number ofhorizontal antenna ports and the oversampling factor and B_v indicatesthe product of the number of vertical antenna ports and the oversamplingfactor.

Here, W_2 can be configured according to Equations 28 and 30 in thecases of rank 1 and rank 2, respectively.

In addition, when W_1 is composed of 8 columns, W_1 can be configured bycombining Equations 43, 44, 45 and 46 and Equations 72 and 73.

For example, a codebook is configured using the pattern of FIG. 25 in asystem using (2,4,2,16), as represented by Equation 75.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{{({{4i_{1}} + 0})}{mod}\; B_{h}} + {B_{h}{\lfloor\frac{i_{1}}{B_{h}\text{/}4}\rfloor}}}\mspace{14mu} w_{{{({{4i_{1}} + 1})}{mod}\; B_{h}} + {B_{h}{\lfloor\frac{i_{1}}{B_{h}\text{/}4}\rfloor}}}\mspace{14mu} \cdots \mspace{14mu} w_{{{({{4i_{1}} + 7})}{mod}\; B_{h}} + {B_{h}{\lfloor\frac{i_{1}}{B_{h}\text{/}4}\rfloor}}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} v_{h}} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{4Q_{h}}} \\e^{j\frac{4\pi \; h}{4Q_{h}}} \\e^{j\frac{6\pi \; h}{4Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{2Q_{v}}}\end{bmatrix}},{v_{m} = {v_{h} \otimes v_{v}}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor},{m \in \left\{ {{\left( {{4i_{1}} + i_{2}} \right){mod}\mspace{14mu} B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}\text{/}4} \right\rfloor}} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},{i_{2} = 0},1,2,\ldots,7}} & \left\lbrack {{Equation}\mspace{14mu} 75} \right\rbrack\end{matrix}$

Here, i_1 indicates the index of W_1 and i_2 is an index correspondingto selection of W_2. B_h indicates the product of the number ofhorizontal antenna ports and the oversampling factor and B_v indicatesthe product of the number of vertical antenna ports and the oversamplingfactor.

Here, W_2 can be configured according to Equation 49 or 54 in the caseof rank 1. W_2 can be configured according to Equation 50, 55 or 56 inthe case of rank 2.

In the above-described embodiments of the present invention, methods ofobtaining DFT vectors and performing kronecker product operation on theDFT vectors to configure codebook vectors on the assumption that thereis no phase offset when DFT vectors of vertical and horizontal elementsare configured have been described.

That is, when an offset is considered in Equations 19 and 20, Equations76 and 77 are obtained.

$\begin{matrix}{{D_{({mn})}^{N_{v} \times N_{v}Q_{v}} = {\frac{1}{\sqrt{N_{v}}}e^{j\frac{{2{\pi {({m - 1})}}{({n - 1})}} + \delta_{v}}{N_{v}Q_{v}}}}},{{{for}\mspace{14mu} m} = 1},2,\cdots,N_{v},{n = 1},2,\cdots,{N_{v}Q_{v}}} & \left\lbrack {{Equation}\mspace{14mu} 76} \right\rbrack \\{{D_{({mn})}^{N_{h} \times N_{h}Q_{h}} = {\frac{1}{\sqrt{N_{v}}}e^{j\frac{{2{\pi {({m - 1})}}{({n - 1})}} + \delta_{h}}{N_{h}Q_{h}}}}},{{{for}\mspace{14mu} m} = 1},2,\cdots,N_{h},{n = 1},2,\cdots,{N_{h}Q_{h}}} & \left\lbrack {{Equation}\mspace{14mu} 77} \right\rbrack\end{matrix}$

Here, δ_(h) and δ_(v) indicate phase offsets of vertical and horizontalDFT vectors, respectively. In embodiments of configuring a codebookconsidering such offsets, a codebook may be configured by settingoffsets when an antenna tilting angle corresponding to a specificcodebook phase is not used.

Furthermore, beam indexes in the horizontal direction in a fat matrix inwhich the number of columns is greater than the number of rows have beenpreferentially described for convenience of description. When beamindexes are arranged in the vertical direction, FIG. 15 can be modifiedinto FIG. 36.

FIG. 36 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

In this case, methods of configuring the entire codebook, W_1 and W_2are the same as the above-described methods, but Equations whichrepresent the methods may be changed according to difference betweenbeam indexing methods. For example, Equation 21 can be modified intoEquation 78.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{w_{{({8i_{1}})}{mod}\; 32{\lfloor\frac{i_{1}}{4}\rfloor}}\mspace{14mu} w_{{({{8i_{1}} + 4})}{mod}\; 32{\lfloor\frac{i_{1}}{4}\rfloor}}\mspace{14mu} w_{{{({{8i_{1}} + 8}\;)}{mod}\; 8} + {\lfloor\frac{i_{1}}{4}\rfloor}}\mspace{14mu} w_{({{8i_{1}} + {12{mod}\; 8{\lfloor\frac{i_{1}}{4}\rfloor}}}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = \left\lfloor \frac{m}{4} \right\rfloor},{v = {m\mspace{14mu} {mod}\mspace{14mu} 4}},{m \in \left\{ {\left( {{8i_{1}} + {4i_{2}}} \right){mod}\mspace{14mu} 32\left\lfloor \frac{i_{1}}{4} \right\rfloor} \right\}},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3,}} & \left\lbrack {{Equation}\mspace{14mu} 78} \right\rbrack\end{matrix}$

Here, i_1 indicates the index of W_1 and i_2 is an index correspondingto selection of W_2.

As in the above-described embodiment, the W_1 configuration methodsdescribed above can also be easily extended and applied when beamindexing is changed to vertical indexing.

In the methods of configuring W_1 described in the present invention, asmany beams as half the number of beams constituting W_1 may overlapbetween W_1s which are adjacent in the horizontal or vertical domain.

That is, in FIGS. 36, W_1(0) and W_1(1) simultaneously include beamscorresponding to indexes 8 and 12. However, a method of configuring W_1without considering overlap may be used.

When overlap occurs in the horizontal domain, only even-numbered indexes{0, 2, 4, 6, . . . } or odd-numbered indexes {1, 3, 5, . . . } may beselected to reconfigure W_1 in a legacy W_1 configuration method.Alternatively, W_1 may be composed of multiples of a specific number,for example, (0, 4, 8, . . . ) in the case of 4.

In the case of design in which overlap occurs in the vertical domain asin the example of FIG. 18, when the number of W_1s composed of the samevertical domain is defined as N_w1, W_1 can be reconfigured usingindexes of {0, 1, . . . , (N_w1)−1, 2N_w1, . . . } in a legacy W_1configuration method to generate W_1s composed of beams without overlaptherebetween. Alternatively, when being moved by a multiple of aspecific number (e.g., 4), W_1 can be constructed by using indexes suchas {0, 1, . . . , (N_w1)−1, 4N_w1, . . . } have.

In the case of methods of configuring W_1 having overlap in the verticalor horizontal domain, beam overlap can be eliminated using theabove-described two principles.

By configuring W_1 in this manner, the number of feedback bits of W_1,L_1, can be reduced.

The above-described embodiments of the present invention propose variouscodebook design methods applicable to the antenna layout shown in FIG.14 for 3D-MIMO. With respect to these codebook design methods, a BS cansignal, to a UE, a codebook to be used by the UE using the followingsignaling methods.

A. The BS can signal the number of antenna ports, such as 8, 12 or 16,to the UE through RRC signaling.

12- and 16-antenna port layouts may respectively have a horizontallylong rectangular form and a vertically long rectangular form, and the BScan signal a codebook suitable for each antenna port layout to the UEthrough RRC signaling using a 1-bit indicator. For example, the UE canrecognize the antenna layout as a horizontally long rectangular antennalayout when the indicator is 0 and recognize the antenna layout as avertically long rectangular antenna layout when the indicator is 1. Inaddition, the UE can generate a codebook suitable for each antennalayout through the 1-bit indicator.

i. Additionally, when a one-dimensional form is considered for antennalayouts (that is, (1,6,2) and (6,1,2) in the case of 12 antenna portsand (1,8,2) and (8,1,2) in the case of 16 antenna ports), the BS cansignal an antenna layout to the UE through RRC signaling using a 2-bitindicator or bitmap. The UE can configure a codebook using the antennalayout.

ii. Additionally, when the UE uses some or all of the above-describedcodebooks, the above-described codebook configuration methods can besignaled to the UE in the form of a bitmap.

iii. In the case of aperiodic CSI reporting, the BS can explicitlysignal L_1 and L_2 which are the numbers of bits corresponding to W_1and W_2 to the UE through RRC signaling or signal the same to the UE inthe form of a bitmap. Then, the UE can configure predetermined codebookscorresponding to the numbers of bits and use the same. In addition, theabove-described codebooks corresponding to L_1 and L_2 may be signaledto the UE in the form of a bitmap such that the UE can generate acodebook.

B. The BS can explicitly signal, to the UE, a method of configuringlayouts corresponding to the numbers of antenna ports, such as 8, 12 and16, that is, the numbers of horizontal and vertical antenna ports. Thatis, the BS can signal information corresponding to (M, N) or (M, N, P)to the UE through RRC signaling and the UE can configure a codebookcorresponding thereto through one of the above-described predeterminedmethods.

i. Additionally, when the UE uses some or all of the above-describedcodebooks, the above-described methods of configuring a codebook can besignaled to the UE in the form of a bitmap.

ii. In the case of aperiodic CSI reporting, the BS can explicitly signalL_1 and L_2 which are the numbers of bits corresponding to W_1 and W_2to the UE through RRC signaling or signal the same to the UE in the formof a bitmap. Then, the UE can configure predetermined codebookscorresponding to the numbers of bits and use the same. In addition, theabove-described codebooks corresponding to L_1 and L_2 may be signaledto the UE in the form of a bitmap such that the UE can generate acodebook.

C. When the number of antenna ports including legacy codebooks is 8, theBS can signal a 1-bit indicator to the UE through RRC signaling. The UEcan generate a legacy codebook or a codebook for (2,2,2) through the1-bit indicator.

i. Additionally, when the UE uses some or all of the above-describedcodebooks, the above-described codebook configuration methods can besignaled to the UE in the form of a bitmap.

ii. In the case of aperiodic CSI reporting, the BS can explicitly signalL_1 and L_2 which are the numbers of bits corresponding to W_1 and W_2to the UE through RRC signaling or signal the same to the UE in the formof a bitmap. Then, the UE can configure predetermined codebookscorresponding to the numbers of bits and use the same. In addition, theabove-described codebooks corresponding to L_1 and L_2 may be signaledto the UE in the form of a bitmap such that the UE can generate acodebook.

In the antenna port layout illustrated in FIG. 14 as an example of a 3DMIMO system, antenna port spacing largely affects codebook design. Thatis, system performance depends on how a codebook is configured when theantenna port spacing is wide (e.g., a physical distance of antenna portvirtualization or antenna elements is long) and when the antenna portspacing is narrow.

In general, it is desirable to configure a beam group of W_1 such thatthe spacing between beams is wide when the spacing between antenna portsis wide and to configure the beam group of W_1 such that the spacingbetween beams is narrow when the spacing between antenna ports isnarrow. For application of codebook design adapted to variousenvironments, the present invention proposes the following methods.

As an embodiment according to the present invention, Equation 32representing that horizontal component beams constituting W_1 areconsecutively grouped for a given vertical component beam can be used.Alternatively, Equation 33 representing that horizontal component beamsare configured while maintaining a specific index group μ=8 (μ may bepredefined or signal to the UE by the BS through RRC signaling) can beused.

When W_1 is composed of 4 beams in (2,4,2,16), equations for configuringa codebook are modified into Equations 79 and 80.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{w_{m{({i_{1},0})}}\mspace{14mu} w_{m{({i_{1},1})}}\mspace{14mu} w_{m{({i_{1},2})}}\mspace{14mu} w_{m{({i_{1},3})}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} v_{h}} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{4Q_{h}}} \\e^{j\frac{4\pi \; h}{4Q_{h}}} \\e^{j\frac{6\pi \; h}{4Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{2Q_{v}}}\end{bmatrix}},{v_{m} = {v_{h} \otimes v_{v}}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor},{{m\left( {i_{1},i_{2}} \right)} = {{{\left( {{2i_{1}} + i_{2}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}\text{/}2} \right\rfloor \mspace{14mu} {for}\mspace{14mu} i_{1}}} = 0}},1,\ldots,{2^{L_{1}} - 1},{i_{2} = 0},1,2,3,}} & \left\lbrack {{Equation}\mspace{14mu} 79} \right\rbrack \\{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{w_{m{({i_{1},0})}}\mspace{14mu} w_{m{({i_{1},1})}}\mspace{14mu} w_{m{({i_{1},2})}}\mspace{14mu} w_{m{({i_{1},3})}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} v_{h}} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{4Q_{h}}} \\e^{j\frac{4\pi \; h}{4Q_{h}}} \\e^{j\frac{6\pi \; h}{4Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{2Q_{v}}}\end{bmatrix}},{v_{m} = {v_{h} \otimes v_{v}}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor},{{m\left( {i_{1},i_{2}} \right)} = {{{\left( {i_{1} + {\mu \; i_{2}}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}\text{/}2} \right\rfloor \mspace{14mu} {for}\mspace{14mu} i_{1}}} = 0}},1,\ldots,{2^{L_{1}} - 1},{i_{2} = 0},1,2,3,}} & \left\lbrack {{Equation}\mspace{14mu} 80} \right\rbrack\end{matrix}$

Here, i_1 indicates the index of W_1 and i_2 is an index correspondingto selection of W_2.

1. The BS can signal a codebook suitable for a spacing between antennaports to the UE through 1-bit signaling. That is, the BS can signalinformation about Equation 79 or 80 to the UE using 1 bit. The UE canreconfigure the codebook using the information.

2. W_1 including Equations 79 and 80 is configured when a codebook isconfigured, which is represented by Equation 81.

$\begin{matrix}{{C_{1} = \left\{ {\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = \left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{w_{m{({i_{1},0})}}\mspace{14mu} w_{m{({i_{1},1})}}\mspace{14mu} w_{m{({i_{1},2})}}\mspace{14mu} w_{m{({i_{1},3})}}} \right\rbrack} \right\}}{{{{where}\mspace{14mu} v_{h}} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{4Q_{h}}} \\e^{j\frac{4\pi \; h}{4Q_{h}}} \\e^{j\frac{6\pi \; h}{4Q_{h}}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{2Q_{v}}}\end{bmatrix}},{v_{m} = {v_{h} \otimes v_{v}}},{h = {{m\left( {i_{1},i_{2}} \right)}\mspace{14mu} {mod}\mspace{14mu} B_{h}}},{v = \left\lfloor \frac{m\left( {i_{1},i_{2}} \right)}{B_{h}} \right\rfloor},\left\{ \begin{matrix}{{{{m\left( {i_{1},i_{2}} \right)} = {{{\left( {{2i_{1}} + i_{2}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}\text{/}2} \right\rfloor \mspace{14mu} {for}\mspace{14mu} i_{1}}} = 0}},1,,{2^{L_{1}} - 1},{i_{2}0},1,2,3,}\mspace{95mu}} \\{{{m\left( {i_{1},i_{2}} \right)} = {{{\left( {i_{1} + {\mu \; i_{2}}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{h}} + {B_{h}\left\lfloor \frac{i_{1}}{B_{h}\text{/}2} \right\rfloor \mspace{14mu} {for}\mspace{14mu} i_{1}}} = 2^{L_{1}}}},1,\ldots,{2^{L_{1} + 1} - 1},{i_{2} = 0},1,2,3}\end{matrix} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 81} \right\rbrack\end{matrix}$

Here, i_1 indicates the index of W_1 and i_2 is an index correspondingto selection of W_2.

In this case, a payload size corresponding to W_1 may increase by 1 bit,but choices of wideband/long-term codebooks of the user can be widened.

3. To prevent the payload size from increasing in the method 2, a methodof subsampling to ½ in Equations 79 and 80 may be used. That is, onlyodd numbers or even numbers can be combined for the index of i_1 inEquations 79 and 80.

4. The proposed method with respect to combination of two codebooksdescribed in 2 may be extended and applied to the above-describedvarious codebook designs in addition to combination of Equations 79 and80.

2D Codebook Design for 16-Port CSI-RS

An embodiment according to the present invention proposes a codebookdesign method for 16 TXRU, as illustrated in FIG. 14(c).

A proposed codebook has a dual codebook structure as represented byEquation 82.

W=W ₁ W ₂  [Equation 82]

Here, W_1 corresponds to long-term and/or wideband channelcharacteristics and W_2 corresponds to short-term and/or subband channelcharacteristics. In addition, W_1 includes two identical sub-matricesindicating beam directivity in two polarization groups and W_2corresponds to beam selection and quantized polarization phase of W_1.According to the double codebook structure, feedback (i.e., long-termfeedback for W_1 and short-term feedback for W_2) overhead can bereduced by setting different feedback periods.

Compared to codebooks of legacy systems, the main difference in codebookdesign for a 2D antenna array is to use additional degrees of freedom inthe vertical domain. To this end, Kronecker product of a horizontal DFTmatrix and a vertical DFT matrix is introduced into W_1 whilemaintaining a block diagonal structure, as represented by the followingequation 83.

$\begin{matrix}{{W_{1}\left( i_{1} \right)} = \begin{bmatrix}{X\left( i_{1} \right)} & 0 \\0 & {X\left( i_{1} \right)}\end{bmatrix}} & \left\lbrack {{Equation}\mspace{14mu} 83} \right\rbrack\end{matrix}$

Here, i₁(i₁=0, . . . , 2^(L) ¹ −1) indicates indexes for W_1 and L₁ isthe number of feedback bits for W_1. X(i₁) is the Kronecker product ofselected columns of horizontal and vertical grids of beams according to

1. Codebook design for W_1

W_1 which is a fat matrix in which the number of columns is greater thanthe number of rows is defined as X=X_(H)⊗X_(V).

Here, X_(H) and X_(V) are fat matrices for the horizontal domain and thevertical domain, respectively.

X_(H) can be configured from an N-Tx DFT vector such as X_(H)=[v_(H,0),v_(H,1), v_(H,2), . . . , v_(H,B) _(H) ⁻¹]. Here, B_(H)=NO_(H) and

$V_{H,k} = {\left\lbrack {1\mspace{14mu} {\exp \left( {j\frac{2\pi \; k}{B_{H}}} \right)}\mspace{14mu} \cdots \mspace{14mu} {\exp \left( {j\frac{2{\pi \left( {N - 1} \right)}k}{B_{H}}} \right)}} \right\rbrack^{T}.}$

O_(H) indicates an oversampling factor in the horizontal domain.

Similarly, X_(V) can be configured from an M-Tx DFT vector such asX_(V)=[v_(V,0), v_(V,1), v_(V,2), . . . v_(V,4O) _(V) ⁻¹]. Here,B_(V)=MO_(V) and

$V_{V,k} = {\left\lbrack {1\mspace{14mu} {\exp \left( {j\frac{2\pi \; k}{B_{V}}} \right)}\mspace{14mu} \cdots \mspace{14mu} {\exp \left( {j\frac{2{\pi \left( {M - 1} \right)}k}{B_{V}}} \right)}} \right\rbrack^{T}.}$

O_(V) indicates an oversampling factor in the vertical domain.

After Kronecker product operation, the total number of beams in fatmatrix X corresponds to B_(T)=B_(H)B_(V)=M·O_(V)·N·O_(H). In addition, Xcan be represented as X=[w₀, w₁, w₂, . . . , w_(B) _(T) ⁻¹]. Here,

$w_{j} = {v_{H,{\lfloor\frac{j}{B_{V}}\rfloor}} \otimes {v_{V,{j\mspace{14mu} {mod}\mspace{14mu} B_{V}}}.}}$

For example, w₁=v_(H,0)⊗v_(V,1).

Feedback overhead for W_1, L_1 is closely related to the oversamplingfactor and the beam group for W_1.

Hereinafter, the following oversampling factors are considered forantenna configurations.

(4,2,2,16): O_V=2, 4, 8 and O_H=8,16

(2,4,2,16): O_V=4, 8, 16 and O_H=8

A method of determining X(i₁) defined as the i₁-th subset of X andrelated to beam grouping of W_1 is proposed.

Three options for configuring X(i₁) on the assumption that X(i₁)includes 4 beams are proposed as follows.

FIG. 37 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Option 1: Horizontal Stripe

Referring to FIG. 37(a), 4 consecutive beams are selected in thehorizontal domain for a given vertical beam. In this option, two beamsoverlap between adjacent X(i₁). In this case, X(i₁) can be determined asrepresented by Equation 84.

$\begin{matrix}{{{X\left( i_{1} \right)} = \left\lbrack {w_{{{({2B_{v}i_{1}})}{mod}\mspace{14mu} B_{T}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}\mspace{14mu} w_{{{({B_{V}{({{2i_{1}} + 1})}})}{mod}\mspace{14mu} B_{T}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}\mspace{14mu} w_{{{({B_{V}{({{2i_{1}} + 2})}})}{mod}\mspace{14mu} B_{T}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}\mspace{14mu} w_{{{({B_{V}{({{2i_{1}} + 3})}})}{mod}\mspace{14mu} B_{T}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}} \right\rbrack}{{{{where}\mspace{14mu} w_{j}} = {v_{H,{\lfloor\frac{j}{B_{V}}\rfloor}} \otimes v_{V,{j\; {mod}\; B_{V}}}}},{j \in \left\{ {{\left( {B_{V}\left( {{2i_{1}} + i_{2}} \right)} \right)\mspace{14mu} {mod}\mspace{14mu} B_{T}} + \left\lfloor \frac{i_{1}}{B_{H}\text{/}2} \right\rfloor} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 84} \right\rbrack\end{matrix}$

Option 2: Rectangle

Referring to FIG. 37(b), two consecutive beams are selected in both thehorizontal domain and the vertical domain. In this option, two beamsoverlap between adjacent X(i₁). In this case, X(i₁) can be determined asrepresented by Equation 85.

$\begin{matrix}{{{X\left( i_{1} \right)} = \left\lbrack {w_{{{({B_{v}i_{1}})}{mod}\mspace{14mu} B_{T}} + {2{\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}}\mspace{14mu} w_{{{({{B_{V}i_{1}} + 1})}{mod}\mspace{14mu} B_{T}} + {2{\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}}\mspace{14mu} w_{{{({B_{V}{({i_{1} + 1})}})}{mod}\mspace{14mu} B_{T}} + {2{\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}}\mspace{14mu} w_{{{({{B_{V}{({i_{1} + 1})}} + 1})}{mod}\mspace{14mu} B_{T}} + {2{\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}}} \right\rbrack}{{{{where}\mspace{14mu} w_{j}} = {v_{H,{\lfloor\frac{j}{B_{V}}\rfloor}} \otimes v_{V,{j\; {mod}\; B_{V}}}}},{j \in \left\{ {{\left( {{B_{V}\left( {i_{1} + \left\lfloor \frac{i_{2}}{2} \right\rfloor} \right)} + {i_{2}\mspace{14mu} {mod}\; 2}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{T}} + {2\left\lfloor \frac{i_{1}}{B_{H}\text{/}2} \right\rfloor}} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 85} \right\rbrack\end{matrix}$

Option 3: Check Pattern

Referring to 37(c), 4 beams are selected one across the one from 8 beamscomposed of 4 consecutive horizontal beams and 2 consecutive verticalbeams. That is, the beams are selected in a check pattern. In thisoption, two beams overlap between adjacent X(i₁). In this case, X(i₁)can be determined as represented by Equation 86.

$\begin{matrix}{{{X\left( i_{1} \right)} = \left\lbrack {w_{{{({2B_{v}i_{1}})}{mod}\mspace{14mu} B_{T}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}\mspace{14mu} w_{{{({{B_{V}{({{2i_{1}} + 1})}} + 1})}{mod}\mspace{14mu} B_{T}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}\mspace{14mu} w_{{{({B_{V}{({{2i_{1}} + 2})}})}{mod}\mspace{14mu} B_{T}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}\mspace{14mu} w_{{{({{B_{V}{({{2i_{1}} + 3})}} + 1})}{mod}\mspace{14mu} B_{T}} + {2{\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}}}} \right\rbrack}{{{{where}\mspace{14mu} w_{j}} = {v_{H,{\lfloor\frac{j}{B_{V}}\rfloor}} \otimes v_{V,{j\; {mod}\; B_{V}}}}},{j \in \left\{ {{\left( {{B_{V}\left( {{2i_{1}} + i_{2}}\; \right)} + {i_{2}\mspace{11mu} {mod}\; 2}} \right)\mspace{14mu} {mod}\mspace{14mu} B_{T}} + \left\lfloor \frac{i_{1}}{B_{H}\text{/}2} \right\rfloor} \right\}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},{i_{2} = 0},1,2,3.}} & \left\lbrack {{Equation}\mspace{14mu} 86} \right\rbrack\end{matrix}$

Options 2 and 3 may have additional degrees of freedom in the verticaldomain compared to option 1.

FIG. 38 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

If 8 beams for X(i₁) are long-term fed back through L₁ bits, theabove-described option 2 (that is, option 4: rectangle pattern in thecase of FIG. 38(a)) and option 3 (that is, option 5: check pattern inthe case of FIG. 38(b)) can be applied. That is, 4 of 8 beams overlapbetween adjacent X(i₁) as shown in FIGS. 38(a) and 38(b).

X(i₁) corresponding to options 4 and 5 can be determined as representedby Equations 87 and 88.

$\begin{matrix}{{{X\left( i_{1} \right)} = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{({{2B_{h}i_{2}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}})}{mod}\; B_{T}}\mspace{14mu} w_{{({{B_{V}{({{2i_{1}} + 1})}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}})}{mod}\; B_{T}}\mspace{14mu} \cdots \mspace{20mu} w_{({{B_{V}{({{2i_{1}} + 3})}} + 1 + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor} - {B_{T}{\lfloor\frac{i_{1}}{{({B_{V} - 1})}B_{H}\text{/}2}\rfloor}{mod}\; B_{T}}}}} \right\rbrack}{{{{where}\mspace{14mu} w_{j}} = {{{v_{H,{\lfloor\frac{j}{B_{V}}\rfloor}} \otimes v_{V,{j\; {mod}\; B_{V}},}}j} \in \left\{ {\left( {{B_{V}\left( {{2i_{1}} + {i_{2}\mspace{14mu} {mod}\; 4}} \right)} + \left\lfloor \frac{i_{2}}{4} \right\rfloor + \left\lfloor \frac{i_{1}}{B_{H}\text{/}2} \right\rfloor - {B_{V}\left\lfloor \frac{i_{2}}{4} \right\rfloor \left\lfloor \frac{i_{1}}{\left( {B_{V} - 1} \right)B_{H}\text{/}2} \right\rfloor}} \right){mod}\mspace{14mu} B_{T}} \right\}}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},{i_{2} = 0},1,2,\ldots,7.}} & \left\lbrack {{Equation}\mspace{14mu} 87} \right\rbrack \\{{{X\left( i_{1} \right)} = \left\lbrack \underset{\underset{8\mspace{14mu} {columns}}{}}{w_{{({{2B_{h}i_{2}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}})}{mod}\; B_{T}}\mspace{14mu} w_{{({{B_{V}{({{2i_{1}} + 1})}} + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor}})} - {B_{T}{\lfloor\frac{i_{1}}{{({B_{T} - 2})}B_{H}\text{/}2}\rfloor}{mod}\; B_{T}}}\mspace{14mu} \cdots \mspace{20mu} w_{({{B_{V}{({{2i_{1}} + 3})}} + 1 + {\lfloor\frac{i_{1}}{B_{H}\text{/}2}\rfloor} - {B_{T}{\lfloor\frac{i_{1}}{{({B_{V} - 1})}B_{H}\text{/}2}\rfloor}{mod}\; B_{T}}}}} \right\rbrack}{{{{where}\mspace{14mu} w_{j}} = {{{v_{H,{\lfloor\frac{j}{B_{V}}\rfloor}} \otimes v_{V,{j\; {mod}\; B_{V}},}}j} \in \left\{ {\left( {{B_{V}\left( {{2i_{1}} + {i_{2}\mspace{14mu} {mod}\; 4}} \right)} + \left\lfloor \frac{i_{2}}{4} \right\rfloor + \left\lfloor \frac{i_{1}}{B_{H}\text{/}2} \right\rfloor - {B_{V}\left\lfloor \frac{i_{2}}{4} \right\rfloor \left\lfloor \frac{i_{1}}{\left( {B_{V} - 1} \right)B_{H}\text{/}2} \right\rfloor}} \right){mod}\mspace{14mu} B_{T}} \right\}}},{i_{1} = 0},1,\ldots,{2^{L_{1}} - 1},{i_{2} = 0},1,2,\ldots,7.}} & \left\lbrack {{Equation}\mspace{14mu} 88} \right\rbrack\end{matrix}$

Consequently, matrix W_1 can be configured using Equation 83 and one ofEquations 84, 85, 86, 87 and 88.

2. Codebook Design for W_2

In options 1, 2 and 3, X(i₁) is composed of 4 beams and thus W_2 may bereused in 3GPP release-12 4Tx codebook.

Accordingly, in the case of rank 1, W_2 can be determined as representedby Equation 89.

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{{\alpha \left( i_{2} \right)}Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{j\; {\alpha \left( i_{2} \right)}Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{{- {\alpha \left( i_{2} \right)}}Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{{- {\alpha \left( i_{2} \right)}}Y}\end{bmatrix}}} \right\}} & \left\lbrack {{Equation}\mspace{14mu} 89} \right\rbrack\end{matrix}$

Here, Yϵ{e₁,e₂,e₃,e₄} and e_((i) ₂ ₊₁₎ is a selection vector having 4elements in which only the (i₂+1)-th element is 1 and the remainingelements are 0. In addition,

${{\alpha \left( i_{2} \right)} = {\exp \left( {j\frac{2{\pi 2}\; i_{2}}{32}} \right)}},{i_{2} = 0},1,2,3,$

is a rotation term for increasing quantization resolution of co-phasingbetween two polarization groups.

In the case of rank 2, W_2 can be determined as represented by Equation90.

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{2}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\}} & \left\lbrack {{Equation}\mspace{14mu} 90} \right\rbrack\end{matrix}$

Here,(Y₁,Y₂)ϵ{(e₁,e₁),(e₂,e₂),(e₃,e₃),(e₄,e₄),(e₁,e₂),(e₂,e₃),(e₁,e₄),(e₂,e₄)}.Accordingly, L₂=4 bits are required for W_2 feedback.

In options 4 and 5, X(i₁) is composed of 8 beams and thus the number ofadditional feedback bits for W_2 increases.

Similarly, in the case of rank 1, W_2 can be determined as representedby Equation 91.

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{{\alpha \left( i_{2} \right)}Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{j\; {\alpha \left( i_{2} \right)}Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{{- {\alpha \left( i_{2} \right)}}Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{{- {\alpha \left( i_{2} \right)}}Y}\end{bmatrix}}} \right\}} & \left\lbrack {{Equation}\mspace{14mu} 91} \right\rbrack\end{matrix}$

Here, Yϵ{e₁,e₂,e₃,e₄,e₅,e₆,e₇,e₈} and e_((i) ₂ ₊₁₎e_((i) ₂ ₊₁₎ is aselection vector having 8 elements in which only the (i₂+1)-th elementis 1 and the remaining elements are 0. In addition,

${{\alpha \left( i_{2} \right)} = {\exp \left( {j\frac{2{\pi 2}\; i_{2}}{32}} \right)}},{i_{2} = 0},1,2,3,4,5,6,{7..}$

In the case of rank 2, W_2 can be determined as represented by Equation92.

$\begin{matrix}{W_{2} \in \left\{ {{\frac{1}{2}\begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \right\}} & \left\lbrack {{Equation}\mspace{14mu} 92} \right\rbrack\end{matrix}$

Here,

$\left( {Y_{1},Y_{2}} \right) \in {\begin{Bmatrix}{\left( {e_{1},e_{1}} \right),\left( {e_{2},e_{2}} \right),\left( {e_{3},e_{3}} \right),\left( {e_{4},e_{4}} \right),\left( {e_{5},e_{5}} \right),\left( {e_{6},e_{6}} \right),\left( {e_{7},e_{7}} \right),\left( {e_{8},e_{8}} \right)} \\{\left( {e_{1},e_{2}} \right),\left( {e_{1},e_{3}} \right),\left( {e_{1},e_{4}} \right),\left( {e_{1},e_{5}} \right),\left( {e_{2},e_{3}} \right),\left( {e_{2},e_{4}} \right),\left( {e_{3},e_{4}} \right),\left( {e_{4},e_{5}} \right)}\end{Bmatrix}.}$

In Equation 92, a selection pair can be acquired by comparing Chordaldistances of all available codebook pairs. In options 4 and 5, 5 bitsare required for short-term feedback (i.e., L₂=5).

3. Performance Evaluation

Performances of Cat-2 baseline and various codebook designs for 16-TXRUare evaluated. For fair comparison, CSI-RS overhead shown in thefollowing table 7 is considered.

Table 7 shows parameters for 2D codebook design.

TABLE 7 Cat-2 Proposed codebook baseline design Number of REs for NZPand ZP CSI- 16*3 16*3 RSs CSI-RS period [ms] 10 10 Mean CSI-RS overhead4.8 4.8 (REs/RB/subframe) CSI-RS de-boosting factor 1 2

Simulation of a CSI-RS de-boosting factor is introduced due to RS powerrestriction in a non-precoded based scheme. A CSI-RS de-boosting factorof 2 indicates power corresponding to half of CSI-RS transmission powerin Cat-2 baseline. In addition, 100 ms feedback period is assumedbecause a scheme based on CSI-RS feedback period increase can provideimproved performance compared to a scheme based on CSI-RS overheadincrease.

Table 8 shows performance of (4, 2, 2, 16) antenna layout of codebookoption 1 in a 3D-UMi (3D-Urban Micro) scenario.

TABLE 8 Mean UE Mean UE 5% UE 5% UE 50% UE FTP load, throughputthroughput throughput throughput throughput Resource λ (bps/Hz) gain(bps/Hz) gain (bps/Hz) utilization (UEs/s/sector) Cat-2 3.083 0.7972.817 0.28 2 baseline 2.006 0.260 1.487 0.59 3 1.344 0.077 0.687 0.84 4O_H = 16, 3.147 2.1% 0.885 11.1% 2.963 0.27 2 O_V = 2 2.199 9.6% 0.35235.1% 1.747 0.53 3 1.535 14.3% 0.115 49.4% 0.930 0.79 4 O_H = 16, 3.1652.7% 0.897 12.6% 2.963 0.27 2 O_V = 4 2.223 10.8% 0.357 37.1% 1.794 0.523 1.569 16.8% 0.122 59.0% 0.990 0.78 4 O_H = 16, 3.175 3.0% 0.909 14.1%3.008 0.26 2 O_V = 8 2.234 11.3% 0.372 43.2% 1.794 0.52 3 1.571 16.9%0.124 60.4% 0.983 0.78 4 O_H = 8, 3.165 2.7% 0.887 11.3% 2.985 0.27 2O_V = 2 2.195 9.4% 0.348 33.6% 1.739 0.53 3 1.540 14.6% 0.113 47.1%0.928 0.79 4 O_H = 8, 3.174 3.0% 0.903 13.3% 2.985 0.27 2 O_V = 4 2.23411.4% 0.363 39.7% 1.810 0.52 3 1.563 16.3% 0.120 55.8% 0.966 0.78 4 O_H= 8, 3.189 3.4% 0.907 13.8% 3.008 0.26 2 O_V = 8 2.234 11.3% 0.364 39.8%1.794 0.52 3 1.573 17.0% 0.122 58.1% 0.978 0.78 4

Table 8 shows comparison results with respect to codebook option 1 and(4, 2, 2, 16) to which various oversampling factors have been applied inthe horizontal and vertical domains in a 3D UMi scenario, and a 3D Uma(3D-Urban Macro) simulation result is shown in Table 15 below. In thesimulation, a CSI-RS port is one-to-one mapped to TXRU. In addition,cell association is based on RSRP (reference signal received power) fromCRS port 0 mapped to the first TXRU, and vertical beam selection marginis assumed to be 3 dB. Detailed evaluation assumption is shown in Table11. As shown in Table 8, a larger oversampling factor provides higherperformance gain. However, when performances with respect to O_H=16 andO_H=8 cases are compared, two factors show similar performances.Particularly, O_H=16 and O_H=8 cases provide up to 16.9% and 60.4% gainscompared to Cat-2 baseline in terms of mean and 5% UE throughput. On theother hand, O_H=8 and O_V=8 cases provide only 17% and 58.1% gains. InTable 12, similar tendency is discovered in (8, 2, 2, 16) having 4 TXRUsper polarization and per column in which a single TXRU is virtualizedinto identical rows having a 100-degree tilting and two adjacent antennaelements in polarization. Accordingly, it may be desirable to selectO_H=8 and O_V=8 in consideration of feedback bits for W_1.

Table 9 shows performance with respect to (2, 4, 2, 16) antenna layoutof codebook option 1 in a 3D-UMi scenario.

TABLE 9 Mean UE Mean UE 5% UE 5% UE 50% UE FTP load, throughputthroughput throughput throughput throughput Resource λ (bps/Hz) gain(bps/Hz) gain (bps/Hz) Utilization (UEs/s/sector) Cat-2 3.419 1.0473.390 0.24 2 baseline 2.587 0.514 2.247 0.45 3 1.913 0.200 1.404 0.7 4O_H = 8, 3.442 0.7% 1.070 2.1% 3.419 0.23 2 O_V = 4 2.609 0.8% 0.5445.8% 2.299 0.44 3 1.942 1.5% 0.222 10.8% 1.434 0.69 4 O_H = 8, 3.4480.9% 1.087 3.8% 3.448 0.23 2 O_V = 8 2.615 1.1% 0.542 5.5% 2.299 0.44 31.950 1.9% 0.224 11.9% 1.444 0.69 4 O_H = 8, 3.445 0.8% 1.090 4.1% 3.4190.23 2 O_V = 16 2.610 0.9% 0.540 5.1% 2.286 0.44 3 1.954 2.1% 0.22311.3% 1.449 0.69 4

Table 9 shows comparison results with respect to codebook option 1 and(2, 4, 2, 16) to which various oversampling factors have been applied inthe vertical domain in the 3D UMi scenario. A simulation result in 3DUma (3D-Urban Macro) is shown in Table 15 below. Results with respect to(4, 4, 2, 16) and (8, 4, 2, 16) having a 100-degree tilting angle arerespectively shown in Tables 13 and 14. In addition, a simulation resultwith respect to a 3D-UMa 500m scenario is shown in Table 16.

Similar to a tall antenna port layout case, a larger oversampling factorprovides higher throughput performance in a fat antenna port layoutcase. In terms of feedback bits for W_1, O_H=8 and O_V=8 require W_1=8bits, whereas O_H=9 and O_V=8 require W_1=9 bits. O_H=8 and O_V=8 canpropose better solutions in both of the tall and fat antenna portlayouts due to marginal performance improvement between the two cases.

Accordingly, it is desirable to determine O_H=8 and O_V=8 asoversampling factors for 16 TXRU in consideration of feedback bits forW_1.

Furthermore, it is desirable to select one of the five options accordingto the present invention for codebook design for a 2D antenna array.

In Table 10, performances of the proposed codebook design options arecompared. In options 1, 2 and 3, W_1 is composed of 4 beams and thusfeedback bits for W_2 are 4 bits. In options 4 and 5, 5 bits arerequired for W_2. Options 2 and 3 provide a slight performance gaincompared to option 1 using short-term vertical beam selection. Whenoptions 1, 4 and 5 are compared, performance gains of up to 2.6% and4.6% can be respectively obtained at mean and 5% UE throughputs whenadditional feedback bits of W_2 are consumed. In codebook options,codebook design based on a check pattern can be satisfactory candidatesfor 16-TXRU owing to excellent performance.

Table 10 shows performance with respect to (4, 2, 2, 16) antenna layoutwhen O_H=8 and O_V=8 are applied in the 3D-UMi scenario.

TABLE 10 Mean UE Mean UE 5% UE 5% UE 50% UE FTP load, ThroughputThroughput Throughput Throughput Throughput Resource λ (bps/Hz) Gain(bps/Hz) Gain (bps/Hz) Utilization (UEs/s/sector) Option 1 3.174 0.9032.985 0.27 2 2.234 0.363 1.810 0.52 3 1.563 0.120 0.966 0.78 4 Option 23.182 0.3% 0.899 −0.4% 3.008 0.26 2 2.233 0.0% 0.367 0.9% 1.810 0.52 31.577 0.9% 0.124 3.0% 0.985 0.78 4 Option 3 3.189 0.5% 0.893 −1.1% 2.9850.26 2 2.243 0.4% 0.365 0.6% 1.810 0.52 3 1.583 1.3% 0.119 −1.2% 0.9780.78 4 Option 4 3.211 1.2% 0.920 1.8% 3.053 0.26 2 2.265 1.4% 0.371 2.2%1.827 0.52 3 1.596 2.1% 0.124 3.7% 1.000 0.78 4 Option 5 3.235 1.9%0.922 2.1% 3.077 0.26 2 2.285 2.3% 0.380 4.6% 1.861 0.51 3 1.603 2.6%0.123 2.8% 1.008 0.78 4

Referring to Table 10, options 2, 3, 4 and 5 can perform short-termvertical selection for given oversampling factors and can be furtheroptimized, distinguished from option 1, and thus they are expected toshow better performance.

Consequently, it is possible to determine O_H=8 and O_V=8 asoversampling factors for 16-TXRU in consideration of feedback bits forW_1.

Furthermore, it is desirable to select one of the five options accordingto the present invention for codebook design for a 2D antenna array.

Table 11 shows simulation parameters and assumption.

TABLE 11 Scenario 3D-UM with ISD (Inter-site distance) = 200 m within 2GHz BS antenna Antenna element configuration: 4 × 2 × 2 (+/−45), 0.5λconfiguration horizontal/0.8 λ vertical antenna spacing UE antenna 2 RxX-pol (0/+90) configuration System bandwidth 10 MHz (50 RBs) UEattachment based on RSRP from CRS port 0 RSRP (formal) Duplex FDDNetwork synchronized synchronization UE distribution conform to TR36.873UE speed 3 km/h Polarized antenna Model-2 of TR36.873 modeling UE arrayorientation ΩUT, α uniformly distributed at angles of [0, 360], ΩUT, β =90 degrees, ΩUT, γ = 0 degree UE antenna pattern Isotropic antenna gainpattern A′(θ′, 

 ′) = 1 Traffic model FTP model 1 having packet size of 0.5 Mbytes (low~20% RU, medium ~50% RU, high ~70% RU) [1] Scheduler Frequency selectivescheduling (multiple UEs per allowed TTI) Receiver Non-ideal channelestimation and interference modeling, detailed guideline conforms toRel-12 [71-12] assumption. LMMSE-IRC receiver, detailed guidelineconforms to Rel-12 [71-12] assumption. CSI-RS, CRS CSI-RS is one-to-onemapped to TXRU, only CRS port 0 is modeled for UE attachment, and CRSport 0 is associamted with the first TXRU. HARQ(Hybrid ARQ) Maximum 4transmission Feedback CQI, PMI and RI reporting is triggered per 10 ms.Feedback delay is 5 ms. Overhead 3 symbols for DL CCHs, 2 CRS ports andDM-RS for 12 REs per PRB Transmission scheme TM10, single CSI process,SU-MIMO (non-CoMP) involving rank adaptation Wrapping methodGeographical distance based Handover margin 3 dB Metrics Mean UEthroughput, 5% UE throughput

Table 12 shows performance with respect to (8, 2, 2, 16) antenna layoutof codebook option 1 in the 3D-UMi scenario.

TABLE 12 Mean UE Mean UE 5% UE 5% UE 50% UE FTP load, ThroughputThroughput Throughput Throughput Throughput Resource λ (bps/Hz) Gain(bps/Hz) Gain (bps/Hz) Utilization (UEs/s/Sector) Cat-2 3.359 0.9643.279 0.25 2 baseline 2.362 0.404 1.914 0.5 3 1.648 0.123 1.031 0.77 4O_H = 8, 3.400 1.2% 1.055 9.5% 3.306 0.24 2 O_V = 2 2.534 7.3% 0.50625.3% 2.198 0.46 3 1.873 13.7% 0.191 55.4% 1.342 0.7 4 O_H = 8, 3.4141.6% 1.070 11.0% 3.361 0.24 2 O_V = 4 2.561 8.4% 0.522 29.3% 2.222 0.453 1.903 15.5% 0.199 62.2% 1.404 0.69 4 O_H = 8, 3.415 1.7% 1.081 12.2%3.348 0.24 2 O_V = 8 2.560 8.4% 0.528 30.6% 2.210 0.45 3 1.908 15.8%0.203 65.0% 1.424 0.69 4

Table 13 shows performance with respect to (4, 4, 2, 16) antenna layoutof codebook option 1 in the 3D-UMi scenario.

TABLE 13 Mean UE Mean UE 5% UE 5% UE 50% UE FTP load, ThroughputThroughput Throughput Throughput Throughput Resource λ (bps/Hz) Gain(bps/Hz) Gain (bps/Hz) Utilization (UEs/s/sector) Cat-2 3.557 1.1123.670 0.22 2 baseline 2.730 0.591 2.454 0.42 3 2.075 0.251 1.587 0.66 4O_H = 8, 3.578 0.6% 1.177 5.8% 3.670 0.22 2 O_V = 4 2.772 1.5% 0.6347.3% 2.516 0.41 3 2.139 3.1% 0.272 8.6% 1.692 0.64 4 O_H = 8, 3.579 0.6%1.173 5.5% 3.636 0.22 2 O_V = 8 2.776 1.7% 0.638 8.1% 2.516 0.41 3 2.1453.3% 0.278 10.9% 1.702 0.63 4 O_H = 8, 3.579 0.6% 1.163 4.5% 3.670 0.222 O_V = 16 2.781 1.9% 0.641 8.5% 2.516 0.41 3 2.150 3.6% 0.279 11.1%1.717 0.63 4

Table 14 shows performance with respect to (8, 4, 2, 16) antenna layoutof codebook option 1 in the 3D-UMi scenario.

TABLE 14 Mean UE Mean UE 5% UE 5% UE 50% UE FTP load, ThroughputThroughput Throughput Throughput Throughput Resource λ (bps/Hz) Gain(bps/Hz) Gain (bps/Hz) Utilization (UEs/s/Sector) Cat-2 3.631 1.1983.810 0.22 2 baseline 2.896 0.654 2.649 0.39 3 2.250 0.300 1.827 0.62 4O_H = 8, 3.681 1.4% 1.282 7.1% 3.922 0.21 2 O_V = 4 2.998 3.5% 0.76316.8% 2.778 0.37 3 2.396 6.5% 0.399 33.1% 2.031 0.57 4 O_H = 8, 3.6821.4% 1.299 8.4% 3.884 0.21 2 O_V = 8 3.007 3.8% 0.771 17.9% 2.797 0.37 32.405 6.9% 0.393 31.3% 2.062 0.57 4 O_H = 8, 3.682 1.4% 1.295 8.1% 3.8840.21 2 O_V = 16 3.007 3.8% 0.771 17.9% 2.797 0.37 3 2.411 7.2% 0.39933.1% 2.051 0.57 4

Table 15 shows performance with respect to (4, 2, 2, 16) antenna layoutof codebook option 1 in the 3D-UMa 500m scenario.

TABLE 15 Mean UE Mean UE 5% UE 5% UE 50% UE FTP load, ThroughputThroughput Throughput Throughput Throughput Resource λ (bps/Hz) Gain(bps/Hz) Gain (bps/Hz) Utilization (UEs/s/Sector) Cat-2 2.479 0.4932.000 0.36 2 baseline 1.490 0.125 0.881 0.73 3 0.961 0.043 0.320 0.89 4O_H = 8, 2.583 4.2% 0.576 16.9% 2.174 0.34 2 O_V = 2 1.659 11.3% 0.17539.4% 1.084 0.68 3 1.071 11.4% 0.055 27.3% 0.408 0.88 4 O_H = 8, 2.6004.9% 0.573 16.2% 2.186 0.34 2 O_V = 4 1.667 11.9% 0.175 39.9% 1.090 0.683 1.075 11.9% 0.056 29.3% 0.418 0.87 4 O_H = 8, 2.593 4.6% 0.582 18.0%2.174 0.34 2 O_V = 8 1.663 11.6% 0.176 40.3% 1.089 0.68 3 4

Table 16 shows performance with respect to (2, 4, 2, 16) antenna layoutof codebook option 1 in the 3D-UMa 500m scenario.

TABLE 16 Mean UE Mean UE 5% UE 5% UE 50% UE FTP load, ThroughputThroughput Throughput Throughput Throughput Resource λ (bps/Hz) Gain(bps/Hz) Gain (bps/Hz) Utilization (UEs/s/sector) Cat-2 2.962 0.7382.721 0.29 2 baseline 2.105 0.315 1.619 0.56 3 1.421 0.096 0.777 0.82 4O_H = 8, 3.020 2.0% 0.797 8.0% 2.797 0.28 2 O_V = 2 2.165 2.8% 0.3387.4% 1.688 0.54 3 1.473 3.6% 0.111 16.1% 0.825 0.8 4 O_H = 8, 3.019 1.9%0.810 9.8% 2.778 0.28 2 O_V = 4 2.165 2.9% 0.339 7.6% 1.709 0.54 3 1.4743.7% 0.109 14.0% 0.823 0.8 4 O_H = 8, 3.016 1.8% 0.802 8.7% 2.778 0.28 2O_V = 8 2.164 2.8% 0.340 7.7% 1.688 0.54 3 4

When the aforementioned check pattern (i.e., configuration with ahorizontal spacing of 2 beams and a vertical spacing of 1 beam betweenW1 beam groups) is used, a case in which a given entire beamN_(h)Q_(h)N_(v)Q_(v) is not included may occur as described in option 3of FIG. 37.

To prevent this, a new check pattern (or zigzag pattern) as shown inFIG. 39 may be used.

FIG. 39 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 39, only the pattern corresponding to odd-numberedindexes of W_1 is reversed to generate the pattern of FIG. 39, asdescribed in option 3 of FIG. 37. Even-numbered indexes of W_1 may bereversed to generate the pattern.

In addition, option 1 shows a horizontal stripe (i.e., two beams overlapin the horizontal direction in identical vertical beams) pattern. If oddnumbers (even numbers) of the vertical indexes or multiples of aspecific number are selected in order to reduce the payload size of W_1in the above pattern, beams with respect to a specific vertical beamcannot be considered.

FIG. 40 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

FIG. 40 illustrates a case in which only even numbers are selected onthe basis of vertical indexes. In this case, beams corresponding toodd-numbered vertical indexes cannot be selected. To solve this problem,a modified horizontal stripe pattern as shown in FIG. 41 may beconsidered.

FIG. 41 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

FIG. 41 illustrates a case in which vertical indexes are increased by 1for odd-numbered indexes of W_1. With this configuration, a largernumber of vertical component beams can be considered compared to thepattern of FIG. 40, and thus performance improvement is expected.

The method described above with reference to FIG. 39 may be equallyapplied to a check pattern configured using a 4×2 rectangle instead ofusing a 2×4 rectangle forming a check pattern.

FIG. 42 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

Referring to FIG. 42, a check pattern (or zigzag pattern) can begeneralized.

This is represented by Equation 93.

$\begin{matrix}{{C_{1} = \left\{ {{\left. \begin{bmatrix}{\overset{\sim}{W}}_{1} & 0 \\0 & {\overset{\sim}{W}}_{1}\end{bmatrix} \middle| {\overset{\sim}{W}}_{1} \right. = {{\left. \quad\left\lbrack \underset{\underset{4\mspace{14mu} {columns}}{}}{w_{{({{{(i_{1})}{mod}\; 10} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}})}{mod}\; 32}\mspace{14mu} w_{{({{{({i_{1} + a})}{mod}\; 8} + {8\; d} + {16{\lfloor\frac{i_{1}}{8}\rfloor}}})}{mod}\; 32}\mspace{14mu} w_{{({{{({i_{1} + 8})}{mod}\; 8} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + {8c}})}{mod}\; 32}\mspace{14mu} w_{({{({i_{1} + {{a{({+ b})}}{mod}\; 8} + {2d} + {16{\lfloor\frac{i_{1}}{8}\rfloor}} + {8c}})}{mod}\; 32}}} \right\rbrack \right\} {where}\mspace{14mu} w_{m}} = {v_{h} \otimes v_{v}}}},{v_{h} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; h}{8}}\end{bmatrix}},{v_{v} = \begin{bmatrix}1 \\e^{j\frac{2\pi \; v}{4}}\end{bmatrix}},{h = {m\; {mod}\; 8}},{v = \left\lfloor \frac{m}{8} \right\rfloor},{m \in {\left\{ {{\left( {i_{1} + {a \cdot \left( {i_{2}\mspace{14mu} {mod}\; 2} \right)} + {b\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\; 8} + {16\left\lfloor \frac{i_{1}}{8} \right\rfloor} + {8{d\left( {i_{2}\mspace{14mu} {mod}\; 2} \right)}} + {8c\left\lfloor \frac{i_{2}}{2} \right\rfloor}} \right){mod}\; 32}}} \right\}},{i_{1} = 0},1,\ldots,15,{i_{2} = 0},1,2,3.} & \left\lbrack {{Equation}\mspace{14mu} 93} \right\rbrack\end{matrix}$

The methods described above with reference to FIGS. 40 and 41 can beequally applied to a vertical stripe pattern obtained by reversing ahorizontal stripe pattern into the vertical domain.

FIG. 43 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

FIG. 43 illustrates a vertical stripe pattern when only even-numberedindexes are selected on the basis of horizontal indexes.

FIG. 44 is a diagram for describing a method of configuring a codebookaccording to an embodiment of the present invention.

FIG. 44 illustrates a vertical stripe pattern when horizontal indexesare increased by 1 for odd-numbered indexes of W_1.

FIG. 45 illustrates a method for transmitting and receiving a signal onthe basis of a codebook according to an embodiment of the presentinvention.

Referring to FIG. 45, an eNB transmits a reference signal (e.g., CSI-RSor the like) to a UE through multiple antenna ports (S4501).

The UE reports channel state information to the eNB (S4502).

Here, the channel state information may include a CQI, an RI, a PMI, aPTI and the like and the UE may derive the CQI, RI, PMI, PTI and thelike using the reference signal received from the eNB.

Particularly, according to the present invention, the PMI may include afirst PMI for selecting a precoding matrix set from a codebook and asecond PMI for selecting one precoding matrix from the precoding matrixset.

Here, the codebook may be configured through the methods described abovewith reference to Equations 19 to 93 and/or FIGS. 15 to 44.

Here, a precoding matrix applied to multiple layers may be configuredprecoding vectors applied to respective layers. Here, each precodingvector applied per layer may be determined in the precoding vector setdetermined by the first PMI and a combination of precoding vectors maybe determined by the second PMI. Here, the precoding vector setdetermined by the first PMI may correspond to a set of precodingmatrices for 1 layer. Accordingly, in the case of multiple layers, aprecoding matrix set may refer to a set of precoding matrices generatedaccording to various combinations of precoding vectors corresponding tothe respective layer.

For example, a codebook may be composed of a precoding matrix generatedon the basis of the Kronecker product of a first matrix for firstdimension (e.g., horizontal dimension) antenna ports and a second matrixfor second dimension (e.g., vertical dimension) antenna ports.

Precoding matrices constituting all codebooks may be represented in a2-dimensional form. In this case, each precoding matrix may be specifiedby an index in the first dimension (i.e., horizontal dimension) and anindex in the second dimension (i.e., vertical dimension). In addition,the first matrix may be specified by the index of the first dimension ofthe precoding matrix and the second matrix may be specified by the indexof the second dimension of the precoding matrix.

In addition, values of first dimension indexes and two dimension indexesof precoding matrices belonging to the precoding matrix set on the basisof the first PMI.

As described above, a precoding matrix set can be configured throughvarious methods. In this case, the eNB can transmit a precoding matrixset configuration method, the number of antenna ports having the samepolarization in the first dimension, the number of antenna ports havingthe same polarization in the second dimension, an oversampling factorused in the first dimension and an oversampling factor used in thesecond dimension to the UE through an RRC (Radio Resource Control)message or the like prior to step S4501.

General Apparatus to which the Present Invention May be Applied

FIG. 46 illustrates a block diagram of a wireless communicationapparatus according to an embodiment of the present invention.

Referring to FIG. 46, the wireless communication system includes a basestation (eNB) 4610 and a plurality of user equipments (UEs) 4620 locatedwithin the region of the eNB 4610.

The eNB 4610 includes a processor 4611, a memory 4612 and a radiofrequency unit 4613. The processor 4611 implements the functions,processes and/or methods proposed in FIGS. 1 to 45 above. The layers ofwireless interface protocol may be implemented by the processor 4611.The memory 4612 is connected to the processor 4611, and stores varioustypes of information for driving the processor 4611. The RF unit 4613 isconnected to the processor 4611, and transmits and/or receives radiosignals.

The UE 4620 includes a processor 4621, a memory 4622 and a radiofrequency unit 4623. The processor 4621 implements the functions,processes and/or methods proposed in FIGS. 1 to 45 above. The layers ofwireless interface protocol may be implemented by the processor 4621.The memory 4622 is connected to the processor 4621, and stores varioustypes of information for driving the processor 4621. The RF unit 4623 isconnected to the processor 4621, and transmits and/or receives radiosignals.

The memories 4612 and 4622 may be located interior or exterior of theprocessors 4611 and 4621, and may be connected to the processors 4611and 4621 with well known means. In addition, the eNB 4610 and/or the UE4620 may have a single antenna or multiple antennas.

The embodiments described so far are those of the elements and technicalfeatures being coupled in a predetermined form. So far as there is notany apparent mention, each of the elements and technical features shouldbe considered to be selective. Each of the elements and technicalfeatures may be embodied without being coupled with other elements ortechnical features. In addition, it is also possible to construct theembodiments of the present invention by coupling a part of the elementsand/or technical features. The order of operations described in theembodiments of the present invention may be changed. A part of elementsor technical features in an embodiment may be included in anotherembodiment, or may be replaced by the elements and technical featuresthat correspond to other embodiment. It is apparent to constructembodiment by combining claims that do not have explicit referencerelation in the following claims, or to include the claims in a newclaim set by an amendment after application.

The embodiments of the present invention may be implemented by variousmeans, for example, hardware, firmware, software and the combinationthereof. In the case of the hardware, an embodiment of the presentinvention may be implemented by one or more application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicro controller, a micro processor, and the like.

In the case of the implementation by the firmware or the software, anembodiment of the present invention may be implemented in a form such asa module, a procedure, a function, and so on that performs the functionsor operations described so far. Software codes may be stored in thememory, and driven by the processor. The memory may be located interioror exterior to the processor, and may exchange data with the processorwith various known means.

It will be understood to those skilled in the art that variousmodifications and variations can be made without departing from theessential features of the inventions. Therefore, the detaileddescription is not limited to the embodiments described above, butshould be considered as examples. The scope of the present inventionshould be determined by reasonable interpretation of the attachedclaims, and all modification within the scope of equivalence should beincluded in the scope of the present invention.

INDUSTRIAL APPLICABILITY

The codebook configuration method in a multi-antenna wirelesscommunication system of the present invention has been described mainlywith the example applied to 3GPP LTE/LTE-A system, but may also beapplied to various wireless communication systems except the 3GPPLTE/LTE-A system.

1. A method for transmitting and receiving a signal by a UE based on acodebook in a 2-dimensional multi-antenna wireless communication system,the method comprising: receiving a channel state information-referencesignal (CSI-RS) from an eNB through multiple antenna ports; andreporting channel state information to the eNB, wherein the channelstate information includes a precoding matrix indicator (PMI), the PMIincludes a first PMI for selecting a precoding matrix set from thecodebook and a second PMI for selecting a precoding matrix from theprecoding matrix set, pairs of indexes of a first dimension and indexesof a second dimension of precoding matrices belonging to the precodingmatrix set are (x,y), (x+2,y), (x+1,y+1) and (x+3,y+1), and x and y areintegers which are not negative numbers, wherein the codebook iscomposed of a precoding matrix generated based on the Kronecker productof a first matrix for first dimension antenna ports and a second matrixfor second dimension antenna ports, and the first matrix is specified bya first dimension index of the precoding matrix and the second matrix isspecified by a second dimension index of the precoding matrix.
 2. Themethod of claim 1, wherein a spacing between precoding matrix setsadjacent in the direction of the first dimension is
 2. 3. (canceled) 4.The method of claim 1, wherein values of first dimension indexes andsecond dimension indexes of precoding matrices belonging to theprecoding matrix set are determined based on the first PMI.
 5. Themethod of claim 1, wherein a factor for controlling phases between afirst polarization antenna port and a second polarization antenna portis determined as one of {1,$\left. {{\exp \left( {j\frac{\pi}{2}} \right)},{\exp \left( {j\frac{2\pi}{2}} \right)},{\exp \left( {j\frac{3\pi}{2}} \right)}} \right\}$based on the second PMI in a cross-polarization antenna.
 6. The methodof claim 1, wherein a total number of precoding matrices constitutingthe codebook is determined by the product of the number of antenna portshaving the same polarization in the first dimension, the number ofantenna ports having the same polarization in the second dimension, anoversampling factor used in the first dimension and an oversamplingfactor used in the second dimension.
 7. The method of claim 1, whereinthe first matrix is composed of one or more columns selected from a DFT(Discrete Fourier Transform) matrix generated according to the equationbelow, $\begin{matrix}{{D_{({mn})}^{N_{h} \times N_{h}Q_{h}} = {\frac{1}{\sqrt{N_{h}}}e^{j\frac{2{\pi {({m - 1})}}{({n - 1})}}{N_{h}Q_{h}}}}},{m = 1},2,\cdots,N_{h},{n = 1},2,\cdots,{N_{h}Q_{h}}} & \lbrack{Equation}\rbrack\end{matrix}$ wherein N_h is the number of antenna ports having the samepolarization in the first dimension and Q_h is an oversampling factorused in the first dimension.
 8. The method of claim 1, wherein thesecond matrix is composed of one or more columns selected from a DFT(Discrete Fourier Transform) matrix generated according to the equationbelow, $\begin{matrix}{{D_{({mn})}^{N_{v} \times N_{v}Q_{v}} = {\frac{1}{\sqrt{N_{v}}}e^{j\frac{2{\pi {({m - 1})}}{({n - 1})}}{N_{v}Q_{v}}}}},{m = 1},2,\cdots,N_{v},{n = 1},2,\cdots,{N_{v}Q_{v}}} & \lbrack{Equation}\rbrack\end{matrix}$ wherein N_v is the number of antenna ports having the samepolarization in the second dimension and Q_v is an oversampling factorused in the second dimension.
 9. A method for transmitting and receivinga signal by an eNB based on a codebook in a 2-dimensional multi-antennawireless communication system, the method comprising: transmitting aCSI-RS to a UE through multiple antenna ports; and receiving channelstate information from the UE, wherein the channel state informationincludes a precoding matrix indicator (PMI), the PMI includes a firstPMI for selecting a precoding matrix set from the codebook and a secondPMI for selecting a precoding matrix from the precoding matrix set,pairs of indexes of a first dimension and indexes of a second dimensionof precoding matrices belonging to the precoding matrix set are (x,y),(x+2,y), (x+1,y+1) and (x+3,y+1), and x and y are integers which are notnegative numbers, wherein the codebook is composed of a precoding matrixgenerated based on the Kronecker product of a first matrix for firstdimension antenna ports and a second matrix for second dimension antennaports, and the first matrix is specified by a first dimension index ofthe precoding matrix and the second matrix is specified by a seconddimension index of the precoding matrix.
 10. The method of claim 9,wherein a spacing between precoding matrix sets adjacent in thedirection of the first dimension is 2.